  
  [1X1 [33X[0;0Y[5Xsingular[105X[101X[1X: the [5XGAP[105X[101X[1X interface to [5XSingular[105X[101X[1X[133X[101X
  
  
  [1X1.1 [33X[0;0YIntroduction[133X[101X
  
  [33X[0;0YThis  is  the  manual  of  the  [5XGAP[105X  package  ``[5Xsingular[105X''  that provides an
  interface  from  the  [5XGAP[105X  computer  algebra system to the [5XSingular[105X computer
  algebra system.[133X
  
  [33X[0;0YThis package allows the [5XGAP[105X user to access functions of [5XSingular[105X from within
  [5XGAP[105X, and to apply these functions to the [5XGAP[105X objects. With this package, the
  user  keeps working with [5XGAP[105X and, if he needs a function of [5XSingular[105X that is
  not  present  in  [5XGAP[105X,  he  can use this function via the interface; see the
  function [2XSingularInterface[102X ([14X1.3-8[114X).[133X
  
  [33X[0;0YThis package provides also a function that computes Groebner bases of ideals
  in  polynomial rings of [5XGAP[105X. This function uses the [5XSingular[105X implementation,
  which is very fast; see the function [2XGroebnerBasis[102X ([14X1.5-1[114X).[133X
  
  [33X[0;0YThe  interface  is  expected to work with every version of [5XGAP[105X 4, every (not
  very  old) version of [5XSingular[105X, and on every platform, on which both [5XGAP[105X and
  [5XSingular[105X run; see paragraph [14X1.7-1[114X for details.[133X
  
  [33X[0;0YIf  you  have used this package in the preparation of a paper please cite it
  as described in [7Xhttps://www.gap-system.org/Contacts/cite.html[107X.[133X
  
  [33X[0;0YIf  [5XGAP[105X,  [5XSingular[105X,  and  the [5XGAP[105X package [5Xsingular[105X are already installed and
  working  on  his computer, the user of this interface needs to read only the
  subsection  [14X1.2-4[114X,  the  section [14X1.3[114X, and in case of problems the subsection
  [14X1.7-4[114X.[133X
  
  
  [1X1.1-1 [33X[0;0YPackage evolution[133X[101X
  
  [33X[0;0YThe  work for the package [5Xsingular[105X has been started by Willem de Graaf, that
  planned  this  package  as  an  interface  to  the function of [5XSingular[105X that
  calculates  the  Groebner  bases. To this purpose, Willem de Graaf wrote the
  code  for  the  conversion of rings and ideals from [5XGAP[105X to [5XSingular[105X, and the
  code for the conversion of numbers and polynomials in both directions.[133X
  
  [33X[0;0YMarco  Costantini  has widened the aim of the package, in order to make it a
  general  interface  to each possible function of [5XSingular[105X: with the function
  [2XSingularInterface[102X ([14X1.3-8[114X) it is possible to use from within [5XGAP[105X any function
  of [5XSingular[105X, including user-defined ones and future implementations. To this
  purpose,  Marco  Costantini  has  generalized  the  previous  code  for  the
  conversion  of objects in the new more general context, has written the code
  for  the  conversion  of the various other types of objects, and has written
  the code for the low-level communication between [5XGAP[105X and [5XSingular[105X.[133X
  
  [33X[0;0YDavid  Joyner  has  developed  the  code  for  the algebraic-geometric codes
  functions, and has written the corresponding section [14X1.6[114X of this manual.[133X
  
  [33X[0;0YGema M. Diaz has helped with some testing and reports.[133X
  
  
  [1X1.1-2 [33X[0;0YThe system [5XSingular[105X[101X[1X[133X[101X
  
  [33X[0;0Y[5XSingular[105X  is [21XA Computer Algebra System for Polynomial Computations[121X developed
  by  G.-M.  Greuel,  G.  Pfister, and H. Sch\"onemann, at Centre for Computer
  Algebra,  University  of  Kaiserslautern.  The  authors  of  the [5XGAP[105X package
  [5Xsingular[105X  are  not  involved  in the development of the system [5XSingular[105X, and
  vice versa.[133X
  
  [33X[0;0Y[5XSingular[105X  is not included in this package, and can be obtained for free from
  [7Xhttps://www.singular.uni-kl.de[107X.  There, one can find also its documentation,
  installing  instructions,  the source code if wanted, and support if needed.
  [5XSingular[105X is available for several platforms.[133X
  
  [33X[0;0YA   description  of  [5XSingular[105X,  copied  from  its  manual  (paragraph  ``2.1
  Background''), version 2-0-5, is the following:[133X
  
  [33X[0;0Y[21X  [5XSingular[105X  is  a  Computer  Algebra system for polynomial computations with
  emphasis  on  the  special needs of commutative algebra, algebraic geometry,
  and singularity theory. [5XSingular[105X's main computational objects are ideals and
  modules  over  a  large  variety  of baserings. The baserings are polynomial
  rings  or  localizations  thereof  over  a  field  (e.g., finite fields, the
  rationals,  floats,  algebraic  extensions,  transcendental  extensions)  or
  quotient  rings  with  respect  to  an  ideal.  [5XSingular[105X features one of the
  fastest and most general implementations of various algorithms for computing
  Groebner  resp.  standard  bases.  The  implementation includes Buchberger's
  algorithm  (if the ordering is a well ordering) and Mora's algorithm (if the
  ordering  is  a  tangent  cone  ordering)  as special cases. Furthermore, it
  provides  polynomial  factorizations,  resultant, characteristic set and gcd
  computations, syzygy and free-resolution computations, and many more related
  functionalities.  Based  on  an  easy-to-use  interactive shell and a C-like
  programming  language,  [5XSingular[105X's  internal  functionality is augmented and
  user-extendible by libraries written in the [5XSingular[105X programming language. A
  general  and efficient implementation of communication links allows [5XSingular[105X
  to   make   its   functionality  available  to  other  programs.  [5XSingular[105X's
  development  started  in  1984 with an implementation of Mora's Tangent Cone
  algorithm  in  Modula-2 on an Atari computer (K.P. Neuendorf, G. Pfister, H.
  Schönemann; Humboldt-Universität zu Berlin). The need for a new system arose
  from  the  investigation  of  mathematical  problems coming from singularity
  theory  which none of the existing systems was able to compute. In the early
  1990s  [5XSingular[105X's  ``home-town'' moved to Kaiserslautern, a general standard
  basis  algorithm  was  implemented  in  C,  and [5XSingular[105X was ported to Unix,
  MS-DOS,  Windows  NT,  and  MacOS.  Continuous  extensions  (like polynomial
  factorization,  gcd  computations, links) and refinements led in 1997 to the
  release  of  [5XSingular[105X  version 1.0 and in 1998 to the release of version 1.2
  (much  faster  standard  and  Groebner  bases  computations based on Hilbert
  series  and  on  improved  implementations  of the algorithms, libraries for
  primary decomposition, ring normalization, etc.). [121X[133X
  
  
  [1X1.1-3 [33X[0;0YThe system [5XGAP[105X[101X[1X[133X[101X
  
  [33X[0;0Y[5XGAP[105X  stands  for  [21XGroups,  Algorithms,  and Programming[121X, and is developed by
  several people ([21XThe [5XGAP[105X Group[121X).[133X
  
  [33X[0;0Y[5XGAP[105X  is  not  included  in  this  package, and can be obtained for free from
  [7Xhttps://www.gap-system.org/[107X.  There,  one  can  find also its documentation,
  installing  instructions,  the  source  code, and support if needed. The [5XGAP[105X
  system  will run on any machine with an Unix-like or recent Windows or MacOS
  operating system and with a reasonable amount of ram and disk space.[133X
  
  [33X[0;0YA  description  of [5XGAP[105X, copied from its web site, is the following: [21X[5XGAP[105X is a
  system  for  computational  discrete  algebra,  with  particular emphasis on
  Computational  Group  Theory. [5XGAP[105X provides a programming language, a library
  of  thousands  of functions implementing algebraic algorithms written in the
  [5XGAP[105X  language  as well as large data libraries of algebraic objects. See the
  web  site the overview and the description of the mathematical capabilities.
  [5XGAP[105X  is  used  in  research  and  teaching  for  studying  groups  and their
  representations,  rings,  vector spaces, algebras, combinatorial structures,
  and more. The system, including source, is distributed freely. You can study
  and easily modify or extend it for your special use.[121X[133X
  
  
  [1X1.2 [33X[0;0YInstallation[133X[101X
  
  [33X[0;0YIn order to use this interface one must have both [5XGAP[105X version 4 and [5XSingular[105X
  installed.[133X
  
  
  [1X1.2-1 [33X[0;0YInstalling the system [5XSingular[105X[101X[1X[133X[101X
  
  [33X[0;0YFollow the [5XSingular[105X installing instructions.[133X
  
  [33X[0;0YHowever, for a Unix system, one needs to download two files:[133X
  
  [30X    [33X[0;6Y[11XSingular-<version>-share.tar.gz[111X,     that     contains    architecture
        independent data like documentation and libraries;[133X
  
  [30X    [33X[0;6Y[11XSingular-<version>-<uname>.tar.gz[111X,    that    contains    architecture
        dependent   executables,  like  the  [5XSingular[105X  program  (precompiled).
        <uname>  is  a  description  of the processor and operating system for
        which [5XSingular[105X is compiled.[133X
  
  [33X[0;0Y[5XSingular[105X specific subdirectories will be created in such a way that multiple
  versions and multiple architecture dependent files of [5XSingular[105X can peaceably
  coexist under the same [11X/usr/local/[111X tree.[133X
  
  [33X[0;0YBefore  trying  the  interface,  make  sure  that  [5XSingular[105X is installed and
  working as stand-alone program.[133X
  
  
  [1X1.2-2 [33X[0;0YInstalling the system [5XGAP[105X[101X[1X[133X[101X
  
  [33X[0;0YFollow the [5XGAP[105X installing instructions.[133X
  
  [33X[0;0YHowever, the basic steps of a [5XGAP[105X installation are:[133X
  
  [30X    [33X[0;6YChoose your preferred archive format and download the archives.[133X
  
  [30X    [33X[0;6YUnpack the archives.[133X
  
  [30X    [33X[0;6YOn Unix: Compile [5XGAP[105X. (Compiled executables for Windows and Mac are in
        the archives.)[133X
  
  [30X    [33X[0;6YOn   Unix:   Some   packages   need   further  installation  for  full
        functionality (which is not available on Windows or Mac).[133X
  
  [30X    [33X[0;6YAdjust some links/scripts/icons ..., depending on your system, to make
        the new version of [5XGAP[105X available to the users of your machine.[133X
  
  [30X    [33X[0;6YOptional: Run a few tests.[133X
  
  [30X    [33X[0;6YOptional, but appreciated: Give some feedback on your installation.[133X
  
  [33X[0;0YThere   is  also  an  experimental  Linux  binary  distribution  via  remote
  synchronization  with  a reference installation, which includes all packages
  and  some  optimizations.  Furthermore,  the  Debian  GNU/Linux distribution
  contains  .deb-packages  with  the  core  part  of  [5XGAP[105X  and some of the [5XGAP[105X
  packages.[133X
  
  
  [1X1.2-3 [33X[0;0YInstalling the package [5Xsingular[105X[101X[1X[133X[101X
  
  [33X[0;0YThe  package  [5Xsingular[105X  is installed and loaded as a normal [5XGAP[105X package: see
  the  [5XGAP[105X documentation [14X'Reference: Installing a GAP Package'[114X and [14X'Reference:
  Loading a GAP Package'[114X.[133X
  
  [33X[0;0YStarting  with  version  4.4  of  [5XGAP[105X,  the  package [5Xsingular[105X is distributed
  together  with  [5XGAP[105X.  Hence,  if  [5XGAP[105X  is  already  installed  with  all the
  distributed  packages, then also the package [5Xsingular[105X is installed. However,
  if  the package [5Xsingular[105X is not included in your [5XGAP[105X installation, it can be
  downloaded  and  unpacked  in the [11Xpkg/[111X directory of the [5XGAP[105X installation. If
  you  don't  have  write  access  to  the  [11Xpkg/[111X  directory  in  your main [5XGAP[105X
  installation  you  can  use  private  directories  as  explained  in the [5XGAP[105X
  documentation  [14X'Reference:  GAP  Root  Directories'[114X.  The  package  [5Xsingular[105X
  doesn't require compilation.[133X
  
  [1X1.2-4 sing_exec[101X
  
  [33X[1;0Y[29X[2Xsing_exec[102X [32X global variable[133X
  [33X[1;0Y[29X[2Xsing_exec_options[102X [32X global variable[133X
  [33X[1;0Y[29X[2XSingularTempDirectory[102X [32X global variable[133X
  
  [33X[0;0YIn  order  to  use the interface, [5XGAP[105X has to be told where to find [5XSingular[105X.
  This can be done in three ways. First, if the [5XSingular[105X executable file is in
  the  search  path,  then  [5XGAP[105X  will  find it. Second, it is possible to edit
  (before   loading   the  package)  one  of  the  first  lines  of  the  file
  [11Xsingular/gap/singular.g[111X  (that  comes  with  this  package).  Third,  it  is
  possible  to  give  the path of the [5XSingular[105X executable file directly during
  each  [5XGAP[105X  session  assigning it to the variable [2Xsing_exec[102X (either before or
  after  this  package  has  been  loaded,  but  before starting [5XSingular[105X with
  [2XStartSingular[102X ([14X1.3-1[114X)), as in the example below.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XLoadPackage( "singular" );[127X[104X
    [4X[28XA GAP interface to Singular, by Marco Costantini and Willem de Graaf[128X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xsing_exec:= "/home/wdg/Singular/2-0-3/ix86-Linux/Singular";;[127X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  directory separator is always '[11X/[111X', even under DOS/Windows or MacOS. The
  value  of  [2Xsing_exec[102X  must  refer  to  the  text-only  version  of  [5XSingular[105X
  ([3XSingular[103X),  and  not  to the Emacs version ([3XESingular[103X), nor to the terminal
  window version ([3XTSingular[103X).[133X
  
  [33X[0;0YIn  a  similar way, it is possible to supply [5XSingular[105X with some command line
  options (or files to read containing user defined functions), assigning them
  to  the  variable  [2Xsing_exec_options[102X.  This  can  be done by editing (before
  loading    the   package)   one   of   the   first   lines   of   the   file
  [11Xsingular/gap/singular.g[111X  (that  comes with this package), or directly during
  each  [5XGAP[105X  session (either before or after this package has been loaded, but
  before  starting  [5XSingular[105X)  with  [2XStartSingular[102X ([14X1.3-1[114X)), as in the example
  below.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XAdd( sing_exec_options, "--no-rc" );[127X[104X
    [4X[25Xgap>[125X [27XAdd( sing_exec_options, "/full_path/my_file" );[127X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  variable [2Xsing_exec_options[102X is initialized to [3X[ "-t" ][103X; the user can add
  further options, but must keep [3X"-t"[103X, which is required. The possible options
  are  described in the [5XSingular[105X documentation, paragraph ``3.1.6 Command line
  options''.[133X
  
  [33X[0;0Y[5XSingular[105X  is  not executed in the current directory, but in a user-specified
  one,  or  in  a  temporary  one.  It  is  possible  to supply this directory
  assigning  it  to  the  variable  [2XSingularTempDirectory[102X. This can be done by
  editing  (before  loading  the  package)  one of the first lines of the file
  [11Xsingular/gap/singular.g[111X  (that  comes with this package), or directly during
  each  [5XGAP[105X  session (either before or after this package has been loaded, but
  before  starting  [5XSingular[105X)  with  [2XStartSingular[102X ([14X1.3-1[114X)), as in the example
  below.  If  [2XSingularTempDirectory[102X is not assigned, [5XGAP[105X will create and use a
  temporary directory, which will be removed when [5XGAP[105X quits.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSingularTempDirectory := Directory( "/tmp" );[127X[104X
    [4X[28Xdir("/tmp/")[128X[104X
  [4X[32X[104X
  
  [33X[0;0YOn  Windows,  [5XSingular[105X  version  3  may be not executed directly, but may be
  executed   as   [3Xbash  Singular[103X.  In  this  case,  the  variables  [2Xsing_exec[102X,
  [2Xsing_exec_options[102X,   [2XSingularTempDirectory[102X   must  reflect  this,  otherwise
  Windows  complains  that [3Xcygwin1.dll[103X is not found. The following works on my
  Windows machine.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XLoadPackage("singular");[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XSingularTempDirectory := Directory("c:/cygwin/bin");[127X[104X
    [4X[28Xdir("c:/cygwin/bin/")[128X[104X
    [4X[25Xgap>[125X [27Xsing_exec := "c:/cygwin/bin/bash.exe";[127X[104X
    [4X[28X"c:/cygwin/bin/bash.exe"[128X[104X
    [4X[25Xgap>[125X [27Xsing_exec_options := [ "Singular", "-t" ];[127X[104X
    [4X[28X[ "Singular", "-t" ][128X[104X
    [4X[25Xgap>[125X [27XStartSingular();[127X[104X
  [4X[32X[104X
  
  [33X[0;0YAnother  possibility  is  to  run  Gap from within the Cygwin shell. In this
  case,  with  a  standard  installation  of Cygwin and [5XSingular[105X, no change is
  required,[133X
  
  
  [1X1.3 [33X[0;0YInteraction with [5XSingular[105X[101X[1X[133X[101X
  
  [33X[0;0YThe  user  must  load  the  package  [5Xsingular[105X  with  [2XLoadPackage[102X ([14XReference:
  LoadPackage[114X).[133X
  
  [1X1.3-1 StartSingular[101X
  
  [33X[1;0Y[29X[2XStartSingular[102X(  ) [32X function[133X
  [33X[1;0Y[29X[2XCloseSingular[102X(  ) [32X function[133X
  
  [33X[0;0YAfter   the   package   [5Xsingular[105X   has  been  loaded,  [5XSingular[105X  is  started
  automatically  when  one  of  the  functions  of  the  interface  is called.
  Alternatively, one can start [5XSingular[105X with the command [3XStartSingular[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XStartSingular();[127X[104X
  [4X[32X[104X
  
  [33X[0;0YSee  [14X1.7-1[114X  for  technical  details.  Explicit  use  of [3XStartSingular[103X is not
  necessary.  If  [3XStartSingular[103X  is called when a previous [5XSingular[105X session is
  running, than session will be closed, and a new session will be started.[133X
  
  [33X[0;0YIf  at  some  point  [5XSingular[105X is no longer needed, then it can be closed (in
  order to save system resources) with the command [3XCloseSingular[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XCloseSingular();[127X[104X
  [4X[32X[104X
  
  [33X[0;0YHowever,  when  [5XGAP[105X  exits, it is expected to close Singular, and remove any
  temporary directory, except in the case of abnormal [5XGAP[105X termination.[133X
  
  [1X1.3-2 SingularHelp[101X
  
  [33X[1;0Y[29X[2XSingularHelp[102X( [3Xtopic[103X ) [32X function[133X
  
  [33X[0;0YHere  [3Xtopic[103X  is  a  string  containing  the  name  of a [5XSingular[105X topic. This
  function provides help on that topic using the [5XSingular[105X help system: see the
  [5XSingular[105X  documentation,  paragraphs  ``3.1.3  The  online help system'' and
  ``5.1.43  help''. If [3Xtopic[103X is the empty string "", then the title/index page
  of the manual is displayed.[133X
  
  [33X[0;0YThis  function  can be used to display the [5XSingular[105X documentation referenced
  in this manual; [3Xtopic[103X must be given without the leading numbers.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSingularHelp( "" ); # a Mozilla window appears[127X[104X
    [4X[28X#I  // ** Displaying help in browser 'mozilla'.[128X[104X
    [4X[28X// ** Use 'system("--browser", <browser>);' to change browser,[128X[104X
    [4X[28X// ** where <browser> can be: "mozilla", "xinfo", "info", "builtin", "dummy", \[128X[104X
    [4X[28X"emacs".[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe   [5XSingular[105X   function   [3Xsystem[103X   can   be   accessed  via  the  function
  [2XSingularInterface[102X  ([14X1.3-8[114X).  Some only-text browsers may be not supported by
  the interface.[133X
  
  
  [1X1.3-3 [33X[0;0YRings and orderings[133X[101X
  
  [33X[0;0YAll  non-trivial  algorithms  in  [5XSingular[105X require the prior definition of a
  (polynomial)  ring,  that  will  be called the ``base-ring''. Any polynomial
  (respectively vector) in [5XSingular[105X is ordered with respect to a term ordering
  (or,  monomial  ordering),  that  has  to  be  specified  together  with the
  declaration  of  a  ring. See the documentation of [5XSingular[105X, paragraph ``3.3
  Rings and orderings'', for further information.[133X
  
  [33X[0;0YAfter  defining  in  [5XGAP[105X a ring, a term ordering can be assigned to it using
  the  function  [2XSetTermOrdering[102X  ([14X1.3-5[114X),  and  [13Xafter[113X  the  term  ordering is
  assigned,  the  interface  and  [5XSingular[105X can be told to use this ring as the
  base-ring, with the function [2XSingularSetBaseRing[102X ([14X1.3-6[114X).[133X
  
  
  [1X1.3-4 [33X[0;0YSupported coefficients fields[133X[101X
  
  [33X[0;0YLet  [3Xp[103X  be  a  prime,  [3Xpol[103X an irreducible polynomial, and [3Xarg[103X an appropriate
  argument for the given function. The coefficient fields of the base-ring may
  be of the following form:[133X
  
  [30X    [33X[0;6Y[3XRationals[103X,[133X
  
  [30X    [33X[0;6Y[3XCyclotomicField( arg )[103X,[133X
  
  [30X    [33X[0;6Y[3XAlgebraicExtension( Rationals, pol )[103X,[133X
  
  [30X    [33X[0;6Y[3XGaloisField( arg )[103X (both prime and non-prime),[133X
  
  [30X    [33X[0;6Y[3XAlgebraicExtension( GaloisField( p ), pol )[103X.[133X
  
  [33X[0;0YFor some example see those for the function [2XSetTermOrdering[102X ([14X1.3-5[114X).[133X
  
  [33X[0;0YLet  us  remember  that  [3XCyclotomicField[103X  and [3XGaloisField[103X can be abbreviated
  respectively  to  [3XCF[103X  and  [3XGF[103X;  these  forms  are  used also when [5XGAP[105X prints
  cyclotomic  or Galois fields. See the [5XGAP[105X documentation about the functions:
  [2XCyclotomicField[102X  ([14XReference:  CyclotomicField for (subfield and) conductor[114X),
  [2XGaloisField[102X  ([14XReference:  GaloisField  for  field  size[114X), [2XAlgebraicExtension[102X
  ([14XReference:  AlgebraicExtension[114X),  and  the  chapters:  [14X'Reference: Rational
  Numbers'[114X,  [14X'Reference:  Abelian  Number Fields'[114X, [14X'Reference: Finite Fields'[114X,
  [14X'Reference: Algebraic extensions of fields'[114X.[133X
  
  [1X1.3-5 SetTermOrdering[101X
  
  [33X[1;0Y[29X[2XSetTermOrdering[102X( [3XR[103X ) [32X function[133X
  [33X[1;0Y[29X[2XTermOrdering[102X( [3XR[103X ) [32X attribute[133X
  
  [33X[0;0YLet  [3XR[103X  be  a  polynomial ring. The value of [3XTermOrdering( R )[103X describes the
  term  ordering  of [3XR[103X, and can be a string, a list, or a monomial ordering of
  [5XGAP[105X.  (The  term  orderings  of [5XSingular[105X are explained in its documentation,
  paragraphs   ``3.3.3   Term   orderings''   and   ``B.2.1   Introduction  to
  orderings''.)[133X
  
  [33X[0;0YIf  this  value  is  a string, for instance [3X"lp"[103X (lexicographical ordering),
  [3X"dp"[103X   (degree   reverse   lexicographical   ordering),   or   [3X"Dp"[103X  (degree
  lexicographical  ordering),  this  value  will be passed to [5XSingular[105X without
  being interpreted or parsed by the interface.[133X
  
  [33X[0;0YIf  this  value  is a list, it must be of the form [3X[ str_1, d_1, str_2, d_2,
  ...  ][103X,  where each [3Xstr_i[103X is a [5XSingular[105X ordering given as a string. Each [3Xd_i[103X
  must  be  a  number,  and  specifies  the  number  of  variables having that
  ordering; however, if [3Xstr_i[103X is a weighted order, like [3X"wp"[103X (weighted reverse
  lexicographical  ordering) or [3X"Wp"[103X (weighted lexicographical ordering), then
  the corresponding [3Xd_i[103X must be a list of positive integers that specifies the
  weight  of  each  variable.  The  sum  of the [3Xd_i[103X's (if numbers) or of their
  lengths (if lists) must be equal to the number of variables of the ring [3XR[103X.[133X
  
  [33X[0;0YThis  value  can also be a monomial ordering of [5XGAP[105X: currently supported are
  [3XMonomialLexOrdering[103X,   [3XMonomialGrevlexOrdering[103X,   and  [3XMonomialGrlexOrdering[103X
  [14X'Reference: Monomial Orderings'[114X.[133X
  
  [33X[0;0Y[3XTermOrdering[103X   is   a  mutable  attribute,  see  the  [5XGAP[105X  documentation  of
  [2XDeclareAttribute[102X  ([14XReference: DeclareAttribute[114X); if it is changed on the [5XGAP[105X
  side,  it  is  necessary  thereafter to send again the ring to [5XSingular[105X with
  [2XSingularSetBaseRing[102X ([14X1.3-6[114X).[133X
  
  [33X[0;0Y[3XSetTermOrdering[103X  can  be  used to set the term ordering of a ring. It is not
  mandatory  to  assign  a term ordering: if no term ordering is set, then the
  default  [3X"dp"[103X  will  be  used.  If  it is set, the term ordering must be set
  [13Xbefore[113X  the  ring  is  sent  to  [5XSingular[105X  with [2XSingularSetBaseRing[102X ([14X1.3-6[114X),
  otherwise,  [5XSingular[105X  will  ignore  that  term  ordering,  and  will use the
  previous value if any, or the default [3X"dp"[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR1:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R1, "lp" );[127X[104X
    [4X[25Xgap>[125X [27XR2:= PolynomialRing( GaloisField(9), 3 );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R2, [ "wp", [1,1,2] ] );[127X[104X
    [4X[25Xgap>[125X [27XR3:= PolynomialRing( CyclotomicField(25), ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R3, MonomialLexOrdering() );[127X[104X
    [4X[25Xgap>[125X [27Xx:=Indeterminate(Rationals);;[127X[104X
    [4X[25Xgap>[125X [27XF:=AlgebraicExtension(Rationals, x^5+4*x+1);;[127X[104X
    [4X[25Xgap>[125X [27XR4:= PolynomialRing( F, 6 );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R4, [ "dp", 1, "wp", [1,1,2], "lp", 2 ] );[127X[104X
  [4X[32X[104X
  
  [1X1.3-6 SingularSetBaseRing[101X
  
  [33X[1;0Y[29X[2XSingularSetBaseRing[102X( [3XR[103X ) [32X function[133X
  [33X[1;0Y[29X[2XSingularBaseRing[102X [32X global variable[133X
  
  [33X[0;0YHere  [3XR[103X  is  a  polynomial  ring.  [3XSingularSetBaseRing[103X sets the base-ring in
  [5XSingular[105X  equal  to  [3XR[103X.  This  ring will be also kept in [5XGAP[105X in the variable
  [3XSingularBaseRing[103X.  After this assignment, all the functions of the interface
  will  work  with this ring. However, for some functions (those having rings,
  ideals,  or  modules as arguments) it is not necessary to explicitly set the
  base  ring  first,  because  in these cases the functions arguments contains
  information  about  a  ring  that  will be used as a base-ring. This will be
  specified  for  each  function  in the corresponding section of this manual.
  (Unnecessary  use  of  [3XSingularSetBaseRing[103X  doesn't  harm; forgetting to use
  [3XSingularSetBaseRing[103X  produces the problem described in the paragraph [14X1.7-4[114X.)
  The  results  of the computations may depend on the choice of the base-ring:
  see  an  example at [2XFactorsUsingSingular[102X ([14X1.5-6[114X), in which the factorization
  of [22Xx^2 + y^2[122X is calculated.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  value of [3XSingularBaseRing[103X when the package is loaded is [3XPolynomialRing(
  GF( 32003 ), 3 )[103X, in order to match the default base-ring of [5XSingular[105X.[133X
  
  [1X1.3-7 SingularLibrary[101X
  
  [33X[1;0Y[29X[2XSingularLibrary[102X( [3Xstring[103X ) [32X function[133X
  
  [33X[0;0YIn  [5XSingular[105X  some functionality is provided by separate libraries that must
  be  explicitly  loaded  in order to be used (see the [5XSingular[105X documentation,
  chapter  ``D.  SINGULAR  libraries''),  see the example in [2XSingularInterface[102X
  ([14X1.3-8[114X).[133X
  
  [33X[0;0YThe  argument  [3Xstring[103X is a string containing the name of a [5XSingular[105X library.
  This function makes sure that this library is loaded into [5XSingular[105X.[133X
  
  [33X[0;0YThe functions provided by the library [3Xring.lib[103X could be not yet supported by
  the interface.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSingularLibrary( "general.lib" );[127X[104X
  [4X[32X[104X
  
  [1X1.3-8 SingularInterface[101X
  
  [33X[1;0Y[29X[2XSingularInterface[102X( [3Xsingcom[103X, [3Xarguments[103X, [3Xtype_output[103X ) [32X function[133X
  
  [33X[0;0YThe  function  [3XSingularInterface[103X provides the general interface that enables
  to  apply  the  [5XSingular[105X functions to the [5XGAP[105X objects. Its arguments are the
  following:[133X
  
  [30X    [33X[0;6Y[3Xsingcom[103X is a [5XSingular[105X command or function (given as a string).[133X
  
  [30X    [33X[0;6Y[3Xarguments[103X  is  a list of [5XGAP[105X objects, [22XO_1, O_2, ..., O_n[122X, that will be
        used as arguments of [3Xsingcom[103X (it may be the empty list). [3Xarguments[103X may
        also  be  a string: in this case it is assumed that it contains one or
        more   [5XSingular[105X  identifiers,  or  a  [5XSingular[105X  valid  expression,  or
        something  else  meaningful for [5XSingular[105X, and it is passed to [5XSingular[105X
        without parsing or checking on the [5XGAP[105X side.[133X
  
  [30X    [33X[0;6Y[3Xtype_output[103X  is  the  data type (given as a string) in [5XSingular[105X of the
        output.   The   data   types  are  the  following  (see  the  [5XSingular[105X
        documentation,  chapter  ``4. Data types''): "bigint", "def", "ideal",
        "int",  "intmat", "intvec", "link", "list", "map", "matrix", "module",
        "number",  "poly",  "proc",  "qring",  "resolution", "ring", "string",
        "vector"  (some  of  them  were  not available in previous versions of
        [5XSingular[105X).  The  empty string "" can be used if no output is expected.
        If  in  doubt  you  can  use  "def"  (see  the [5XSingular[105X documentation,
        paragraph ``4.1 def''). Usually, in the documentation of each [5XSingular[105X
        function is given its output type.[133X
  
  [33X[0;0YOf  course,  the  objects  in the list [3Xarguments[103X and the [3Xtype_output[103X must be
  appropriate for the function [3Xsingcom[103X: no check is done by the interface.[133X
  
  [33X[0;0YThe function [3XSingularInterface[103X does the following:[133X
  
  [31X1[131X   [33X[0;6Yconverts  each  object  [22XO_1,  O_2,  ...,  O_n[122X  in  [3Xarguments[103X  into the
        corresponding object [22XP_1, P_2, ..., P_n[122X, of [5XSingular[105X,[133X
  
  [31X2[131X   [33X[0;6Ysends  to  [5XSingular[105X  the command to calculate [22Xsingcom ( P_1, P_2, ...,
        P_n )[122X,[133X
  
  [31X3[131X   [33X[0;6Ygets the output (of type [3Xtype_output[103X) from [5XSingular[105X,[133X
  
  [31X4[131X   [33X[0;6Yconverts  it  to  the  corresponding Gap object, and returns it to the
        user.[133X
  
  [33X[0;0YThe     function     [3XSingularInterface[103X     is     oriented    towards    the
  kind-of-objects/data-types, and not to the functions of [5XSingular[105X, because in
  this  way  it  is  much  more general. The user can use ``all'' the existing
  functions  of  [5XSingular[105X  and  the  interface  is not bounded to the state of
  implementation of [5XSingular[105X: future functions and user-defined functions will
  be automatically supported.[133X
  
  [33X[0;0YThe  conversion  of  objects from Gap to [5XSingular[105X and from it back to Gap is
  done  using  some  `ad  hoc' functions. Currently, the conversion of objects
  from [5XGAP[105X to [5XSingular[105X is implemented for the following types: "ideal", "int",
  "intmat",  "intvec",  "list",  "matrix", "module", "number", "poly", "ring",
  "string",  "vector".  Objects  of other types are not supported, or are even
  not yet implemented in [5XGAP[105X.[133X
  
  [33X[0;0YThe  conversion of objects from [5XSingular[105X to [5XGAP[105X is currently implemented for
  the  following  types:  "bigint", "def", "ideal", "int", "intmat", "intvec",
  "list",   "matrix",   "module",  "number",  "poly",  "proc"  (experimental),
  "string", "vector". Objects of other types are returned as strings.[133X
  
  [33X[0;0YBefore passing polynomials (or numbers, vectors, matrices, or lists of them)
  to [5XSingular[105X, it is necessary to have sent the base-ring to [5XSingular[105X with the
  function [2XSingularSetBaseRing[102X ([14X1.3-6[114X), in order to ensure that [5XSingular[105X knows
  about them. This is not necessary if in the input there is a ring, an ideal,
  or  a  module  (before  the  polynomials),  because  these  objects  contain
  information  about  the  ring to be used as base-ring. All the input must be
  relative to at most one ring; furthermore, at most one object of type "ring"
  can be in the input.[133X
  
  [33X[0;0YAs SingularInterface is a rather general function, it is not guaranteed that
  it  always  works,  and  some  functions are not supported. For instance, in
  [5XSingular[105X  there  is  the  function  [3Xpause[103X  that  waits  until a keystroke is
  pressed;  but  the  interface  instead  waits for the [5XSingular[105X prompt before
  sending it any new keystroke, and so calling [3Xpause[103X would hang the interface.
  However,  the  unsupported  functions like [3Xpause[103X are only a few, and are not
  mathematically  useful.  SingularInterface  tries  to  block  calls to known
  unsupported functions.[133X
  
  [33X[0;0YSome  [5XSingular[105X  functions  may  return more than one value, see the [5XSingular[105X
  documentation,  paragraph  ``6.2.7  Return type of procedures''. In order to
  use  one of these functions via [3XSingularInterface[103X, the type [3Xtype_output[103X must
  be  "list".  The output in [5XGAP[105X will be a list containing the values returned
  by the [5XSingular[105X function.[133X
  
  [33X[0;0YIn  the  next example we compute the primary decomposition of an ideal. Note
  that for that we need to load the [5XSingular[105X library [3Xprimdec.lib[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27Xi:= IndeterminatesOfPolynomialRing(R);;[127X[104X
    [4X[25Xgap>[125X [27Xx:= i[1];; y:= i[2];; z:= i[3];;[127X[104X
    [4X[25Xgap>[125X [27Xf:= (x*y-z)*(x*y*z+y^2*z+x^2*z);;[127X[104X
    [4X[25Xgap>[125X [27Xg:= (x*y-z)*(x*y*z^2+x*y^2*z+x^2*y*z);;[127X[104X
    [4X[25Xgap>[125X [27XI:= Ideal( R, [f,g] );;[127X[104X
    [4X[25Xgap>[125X [27XSingularLibrary( "primdec.lib" );[127X[104X
    [4X[25Xgap>[125X [27XSingularInterface( "primdecGTZ", [ I ], "def" );[127X[104X
    [4X[28X#I  Singular output of type "list"[128X[104X
    [4X[28X[ [ <two-sided ideal in Rationals[x,y,z], (1 generator)>,[128X[104X
    [4X[28X      <two-sided ideal in Rationals[x,y,z], (1 generator)> ],[128X[104X
    [4X[28X  [ <two-sided ideal in Rationals[x,y,z], (1 generator)>,[128X[104X
    [4X[28X      <two-sided ideal in Rationals[x,y,z], (1 generator)> ],[128X[104X
    [4X[28X  [ <two-sided ideal in Rationals[x,y,z], (2 generators)>,[128X[104X
    [4X[28X      <two-sided ideal in Rationals[x,y,z], (2 generators)> ],[128X[104X
    [4X[28X  [ <two-sided ideal in Rationals[x,y,z], (3 generators)>,[128X[104X
    [4X[28X      <two-sided ideal in Rationals[x,y,z], (2 generators)> ] ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YIn  the next example are calculated the first syzygy module of an ideal, and
  the  resultant of two polynomials with respect a variable. Note that in this
  case  it  is  not  necessary  to  set the base-ring with [2XSingularSetBaseRing[102X
  ([14X1.3-6[114X),  in  the  first case because the input [3XI[103X is of type "ideal", and in
  the  second  case  because the base-ring was already sent to [5XSingular[105X in the
  former case.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27Xi:= IndeterminatesOfPolynomialRing( R );;[127X[104X
    [4X[25Xgap>[125X [27Xx:= i[1];; y:= i[2];; z:= i[3];;[127X[104X
    [4X[25Xgap>[125X [27Xf:= 3*(x+2)^3+y;;[127X[104X
    [4X[25Xgap>[125X [27Xg:= x+y+z;;[127X[104X
    [4X[25Xgap>[125X [27XI:= Ideal( R, [f,g] );;[127X[104X
    [4X[25Xgap>[125X [27XM := SingularInterface( "syz", [ I ], "module" );;[127X[104X
    [4X[25Xgap>[125X [27XGeneratorsOfLeftOperatorAdditiveGroup( M );[127X[104X
    [4X[28X[ [ -x-y-z, 3*x^3+18*x^2+36*x+y+24 ] ][128X[104X
    [4X[25Xgap>[125X [27XSingularInterface( "resultant", [ f, g, z ], "poly");[127X[104X
    [4X[28X3*x^3+18*x^2+36*x+y+24[128X[104X
  [4X[32X[104X
  
  [1X1.3-9 SingularType[101X
  
  [33X[1;0Y[29X[2XSingularType[102X( [3Xobj[103X ) [32X function[133X
  
  [33X[0;0Yto be written[133X
  
  
  [1X1.4 [33X[0;0YInteraction with [5XSingular[105X[101X[1X at low level[133X[101X
  
  [1X1.4-1 SingularCommand[101X
  
  [33X[1;0Y[29X[2XSingularCommand[102X( [3Xprecommand[103X, [3Xcommand[103X ) [32X function[133X
  
  [33X[0;0Yto be written[133X
  
  [1X1.4-2 GapInterface[101X
  
  [33X[1;0Y[29X[2XGapInterface[102X( [3Xfunc[103X, [3Xarg[103X, [3Xout[103X ) [32X function[133X
  
  [33X[0;0Yto be written[133X
  
  
  [1X1.5 [33X[0;0YOther mathematical functions of the package[133X[101X
  
  [1X1.5-1 GroebnerBasis[101X
  
  [33X[1;0Y[29X[2XGroebnerBasis[102X( [3XI[103X ) [32X operation[133X
  
  [33X[0;0YHere  [3XI[103X  is an ideal of a polynomial ring. This function computes a Groebner
  basis  of  [3XI[103X  (that  will  be  returned  as a list of polynomials). For this
  function  it  is [13Xnot[113X necessary to set the base-ring with [2XSingularSetBaseRing[102X
  ([14X1.3-6[114X).[133X
  
  [33X[0;0YAs term ordering, [5XSingular[105X will use the value of [2XTermOrdering[102X ([14X1.3-5[114X) of the
  polynomial  ring  containing  [3XI[103X.  Again,  if this value is not set, then the
  degree reverse lexicographical ordering ([3X"dp"[103X) will be used.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27Xx := R.1;; y := R.2;; z := R.3;;[127X[104X
    [4X[25Xgap>[125X [27Xr:= [ x*y*z -x^2*z, x^2*y*z-x*y^2*z-x*y*z^2, x*y-x*z-y*z ];;[127X[104X
    [4X[25Xgap>[125X [27XI:= Ideal( R, r );[127X[104X
    [4X[28X<two-sided ideal in Rationals[x,y,z], (3 generators)>[128X[104X
    [4X[25Xgap>[125X [27XGroebnerBasis( I );[127X[104X
    [4X[28X[ x*y-x*z-y*z, x^2*z-x*z^2-y*z^2, x*z^3+y*z^3, -x*z^3+y^2*z^2-y*z^3 ][128X[104X
  [4X[32X[104X
  
  [1X1.5-2 SINGULARGBASIS[101X
  
  [33X[1;0Y[29X[2XSINGULARGBASIS[102X [32X global variable[133X
  
  [33X[0;0YThis  variable  is a record containing the component [3XGroebnerBasis[103X. When the
  variable  SINGULARGBASIS is assigned to the [5XGAP[105X global variable [3XGBASIS[103X, then
  the  computations  of  Groebner  bases via [5XGAP[105X's internal function for that,
  [2XGroebnerBasis[102X ([14XReference: GroebnerBasis[114X), are done by [5XSingular[105X.[133X
  
  [33X[0;0Y[5XSingular[105X  claims  that  it  [21Xfeatures  one  of  the  fastest and most general
  implementations  of  various  algorithms  for  computing Groebner bases[121X. The
  [5XGAP[105X's  internal  function  claims  to  be  [21Xa  na{\"\i}ve  implementation  of
  Buchberger's  algorithm  (which  is  mainly intended as a teaching tool): it
  might not be sufficient for serious problems.[121X[133X
  
  [33X[0;0Y(Note in the following example that the Groebner bases calculated by the [5XGAP[105X
  internal  function are in general not reduced; for reduced bases see the [5XGAP[105X
  function [2XReducedGroebnerBasis[102X ([14XReference: ReducedGroebnerBasis[114X).)[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, 3 );;[127X[104X
    [4X[25Xgap>[125X [27Xi:= IndeterminatesOfPolynomialRing( R );;[127X[104X
    [4X[25Xgap>[125X [27Xpols:= [i[1]+i[2]+i[3], i[1]*i[2]+i[1]*i[3]+i[2]*i[3], i[1]*i[2]*i[3]];;[127X[104X
    [4X[25Xgap>[125X [27Xo:= MonomialLexOrdering();;[127X[104X
    [4X[25Xgap>[125X [27XGBASIS:= GAPGBASIS;;[127X[104X
    [4X[25Xgap>[125X [27XGroebnerBasis( pols, o ); # This is the internal GAP method.[127X[104X
    [4X[28X[ x+y+z, x*y+x*z+y*z, x*y*z, -y^2-y*z-z^2, z^3 ][128X[104X
    [4X[25Xgap>[125X [27XGBASIS:= SINGULARGBASIS;;[127X[104X
    [4X[25Xgap>[125X [27XGroebnerBasis( pols, o ); # This uses Singular via the interface.[127X[104X
    [4X[28X[ z^3, y^2+y*z+z^2, x+y+z ][128X[104X
  [4X[32X[104X
  
  [1X1.5-3 HasTrivialGroebnerBasis[101X
  
  [33X[1;0Y[29X[2XHasTrivialGroebnerBasis[102X( [3XI[103X ) [32X function[133X
  
  [33X[0;0YThe  function  [3XHasTrivialGroebnerBasis[103X returns [3Xtrue[103X if the Groebner basis of
  the  ideal [3XI[103X is trivial, false otherwise. This function can be used if it is
  not  necessary  to  know  the Groebner basis of an ideal, but it suffices to
  know only whether it is trivial or not.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xx:= Indeterminate( Rationals, "x" : old );;[127X[104X
    [4X[25Xgap>[125X [27Xy:= Indeterminate( Rationals, "y", [ x ] : old );;[127X[104X
    [4X[25Xgap>[125X [27Xz:= Indeterminate( Rationals, "z", [ x, y ] : old );;[127X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, [ x, y, z] );;[127X[104X
    [4X[25Xgap>[125X [27Xf:= (x*y-z)*(x*y*z+y^2*z+x^2*z);;[127X[104X
    [4X[25Xgap>[125X [27Xg:= (x*y-z)*(x*y*z^2+x*y^2*z+x^2*y*z);;[127X[104X
    [4X[25Xgap>[125X [27XI:= Ideal( R, [f,g] );;[127X[104X
    [4X[25Xgap>[125X [27XHasTrivialGroebnerBasis( I );[127X[104X
    [4X[28Xfalse[128X[104X
  [4X[32X[104X
  
  [1X1.5-4 GcdUsingSingular[101X
  
  [33X[1;0Y[29X[2XGcdUsingSingular[102X( [3Xpol_1[103X, [3Xpol_2[103X, [3X...[103X, [3Xpol_n[103X ) [32X function[133X
  [33X[1;0Y[29X[2XGcdUsingSingular[102X( [[3Xpol_1[103X, [3Xpol_2[103X, [3X...[103X, [3Xpol_n[103X] ) [32X function[133X
  
  [33X[0;0YThe  arguments  of  this  function  are  (possibly multivariate) polynomials
  separated  by  commas, or it is a list of polynomials. This function returns
  the  greatest  common  divisor of these polynomials. For this function it is
  [13Xnecessary[113X   for  the  polynomials  to  lie  in  the  base-ring,  as  set  by
  [2XSingularSetBaseRing[102X ([14X1.3-6[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
    [4X[25Xgap>[125X [27Xi:= IndeterminatesOfPolynomialRing(R);;[127X[104X
    [4X[25Xgap>[125X [27Xx:= i[1];; y:= i[2];; z:= i[3];;[127X[104X
    [4X[25Xgap>[125X [27Xf:= (x*y-z)*(x*y*z+y^2*z+x^2*z);[127X[104X
    [4X[28Xx^3*y*z+x^2*y^2*z+x*y^3*z-x^2*z^2-x*y*z^2-y^2*z^2[128X[104X
    [4X[25Xgap>[125X [27Xg:= (x*y-z)*(x*y*z^2+x*y^2*z+x^2*y*z);[127X[104X
    [4X[28Xx^3*y^2*z+x^2*y^3*z+x^2*y^2*z^2-x^2*y*z^2-x*y^2*z^2-x*y*z^3[128X[104X
    [4X[25Xgap>[125X [27XGcdUsingSingular( f, g );[127X[104X
    [4X[28X-x*y*z+z^2[128X[104X
  [4X[32X[104X
  
  [1X1.5-5 FactorsUsingSingularNC[101X
  
  [33X[1;0Y[29X[2XFactorsUsingSingularNC[102X( [3Xf[103X ) [32X function[133X
  
  [33X[0;0YHere  [3Xf[103X  is  a (possibly multivariate) polynomial. This function returns the
  factorization of [3Xf[103X into irreducible factors. The first element in the output
  is  a constant coefficient, and the others may be monic (with respect to the
  term ordering) polynomials, as returned by [5XSingular[105X. For this function it is
  [13Xnecessary[113X  that  [3Xf[103X  lies  in  the  base-ring,  as set by [2XSingularSetBaseRing[102X
  ([14X1.3-6[114X).[133X
  
  [33X[0;0YThe  function  does not check that the product of these factors gives [3Xf[103X (for
  that  use  [2XFactorsUsingSingular[102X  ([14X1.5-6[114X)): [5XSingular[105X version 2-0-3 contains a
  bug  so  that  the  [5XSingular[105X  function  [3Xfactorize[103X  may  give  wrong  results
  (therefore [5XSingular[105X version at least 2-0-4 is recommended).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y","z"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
    [4X[25Xgap>[125X [27Xi:= IndeterminatesOfPolynomialRing( R );;[127X[104X
    [4X[25Xgap>[125X [27Xx:= i[1];; y:= i[2];; z:= i[3];;[127X[104X
    [4X[25Xgap>[125X [27Xf:= (x*y-z)*(3*x*y*z+4*y^2*z+5*x^2*z);[127X[104X
    [4X[28X5*x^3*y*z+3*x^2*y^2*z+4*x*y^3*z-5*x^2*z^2-3*x*y*z^2-4*y^2*z^2[128X[104X
    [4X[25Xgap>[125X [27XFactorsUsingSingularNC( f );[127X[104X
    [4X[28X[ 1, -5*x^2-3*x*y-4*y^2, -x*y+z, z ][128X[104X
    [4X[25Xgap>[125X [27Xf:= (x*y-z)*(5/3*x*y*z+4*y^2*z+6*x^2*z);[127X[104X
    [4X[28X6*x^3*y*z+5/3*x^2*y^2*z+4*x*y^3*z-6*x^2*z^2-5/3*x*y*z^2-4*y^2*z^2[128X[104X
    [4X[25Xgap>[125X [27XFactorsUsingSingularNC( f );[127X[104X
    [4X[28X[ 1/3, -18*x^2-5*x*y-12*y^2, -x*y+z, z ][128X[104X
  [4X[32X[104X
  
  [1X1.5-6 FactorsUsingSingular[101X
  
  [33X[1;0Y[29X[2XFactorsUsingSingular[102X( [3Xf[103X ) [32X function[133X
  
  [33X[0;0YThis does the same as [2XFactorsUsingSingularNC[102X ([14X1.5-5[114X), except that on the [5XGAP[105X
  level  it  is checked that the product of these factors gives [3Xf[103X. Again it is
  [13Xnecessary[113X  that  [3Xf[103X  lies  in  the  base-ring,  as set by [2XSingularSetBaseRing[102X
  ([14X1.3-6[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( Rationals, ["x","y"] : old );;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
    [4X[25Xgap>[125X [27Xx := R.1;; y := R.2;;[127X[104X
    [4X[25Xgap>[125X [27XFactorsUsingSingular( x^2 + y^2 );[127X[104X
    [4X[28X[ 1, x^2+y^2 ][128X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( GaussianRationals, ["x","y"] : old);;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
    [4X[25Xgap>[125X [27Xx := R.1;; y := R.2;;[127X[104X
    [4X[25Xgap>[125X [27XFactorsUsingSingular( x^2 + y^2 );[127X[104X
    [4X[28X[ 1, x+E(4)*y, x-E(4)*y ][128X[104X
  [4X[32X[104X
  
  [1X1.5-7 GeneratorsOfInvariantRing[101X
  
  [33X[1;0Y[29X[2XGeneratorsOfInvariantRing[102X( [3XR[103X, [3XG[103X ) [32X function[133X
  
  [33X[0;0YHere  [3XR[103X is a polynomial ring, and [3XG[103X a finite group, which is either a matrix
  group  or  a permutation group. If [3XG[103X is a matrix group, then its degree must
  be  less  than  or  equal  to  the  number of indeterminates of [3XR[103X. If [3XG[103X is a
  permutation  group,  then its maximal moved point must be less than or equal
  to  the  number  of  indeterminates  of  [3XR[103X. This function computes a list of
  generators  of  the  invariant  ring of [3XG[103X, corresponding to its action on [3XR[103X.
  This action is taken to be from the left.[133X
  
  [33X[0;0YFor   this   function  it  is  [13Xnot[113X  necessary  to  set  the  base-ring  with
  [2XSingularSetBaseRing[102X ([14X1.3-6[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xm:=[[1,1,1],[0,1,1],[0,0,1]] * One( GF(3) );;[127X[104X
    [4X[25Xgap>[125X [27XG:= Group( [m] );;[127X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( GF(3), 3 );;[127X[104X
    [4X[25Xgap>[125X [27XGeneratorsOfInvariantRing( R, G );[127X[104X
    [4X[28X[ x_3, x_1*x_3+x_2^2+x_2*x_3, x_1^3+x_1^2*x_3-x_1*x_2^2-x_1*x_2*x_3 ][128X[104X
  [4X[32X[104X
  
  
  [1X1.6 [33X[0;0YAlgebraic-geometric codes functions[133X[101X
  
  [33X[0;0YThis  section  of  [5XGAP[105X's  [5Xsingular[105X  package  and the corresponding code were
  written  by  David  Joyner,  [7Xmailto:wdj@usna.edu[107X,  (with help from Christoph
  Lossen  and  Marco  Costantini).  It  has  been tested with [5XSingular[105X version
  2.0.x.[133X
  
  [33X[0;0YTo  start  off,  several new [5XSingular[105X commands must be loaded. The following
  command loads the necessary [5XSingular[105X and [5XGAP[105X commands, the packages [5Xsingular[105X
  and [5XGUAVA[105X (if not already loaded), and (re)starts [5XSingular[105X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XReadPackage("singular", "contrib/agcode.g");;[127X[104X
  [4X[32X[104X
  
  [1X1.6-1 AllPointsOnCurve[101X
  
  [33X[1;0Y[29X[2XAllPointsOnCurve[102X( [3Xf[103X, [3XF[103X ) [32X function[133X
  
  [33X[0;0YLet  [22XF[122X  be  a  finite and prime field. The function [3XAllPointsOnCurve( f, F )[103X
  computes  a  list  of  generators  of  maximal ideals representing rationals
  points on a curve [22XX[122X defined by [22Xf(x,y)=0[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XF:=GF(7);;[127X[104X
    [4X[25Xgap>[125X [27XR2:= PolynomialRing( F, 2 );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R2, "lp" );; # --- the term ordering must be "lp"[127X[104X
    [4X[25Xgap>[125X [27Xindet:= IndeterminatesOfPolynomialRing(R2);;[127X[104X
    [4X[25Xgap>[125X [27Xx:= indet[1];; y:= indet[2];;[127X[104X
    [4X[25Xgap>[125X [27Xf:=x^7-y^2-x;;[127X[104X
    [4X[25Xgap>[125X [27XAllPointsOnCurve(f,F);[127X[104X
    [4X[28X[ [ x_1 ], [ x_1-Z(7)^0 ], [ x_1+Z(7)^4 ], [ x_1+Z(7)^5 ], [ x_1+Z(7)^0 ], [128X[104X
    [4X[28X  [ x_1+Z(7) ], [ x_1+Z(7)^2 ] ][128X[104X
  [4X[32X[104X
  
  [1X1.6-2 AGCode[101X
  
  [33X[1;0Y[29X[2XAGCode[102X( [3Xf[103X, [3XG[103X, [3XD[103X ) [32X function[133X
  
  [33X[0;0YLet f be a polynomial in x,y over F=GF(p) representing plane curve [22XX[122X defined
  by  [22Xf(x,y)=0[122X,  where p is a prime (prime powers are not yet supported by the
  underlying  [5XSingular[105X function). Let G, D be disjoint rational divisors on [22XX[122X,
  where  D  is  a  sum  of distinct points, [22Xsupp(D)=P_1, ..., P_n[122X. The AG code
  associated to f, G, D is the F defined to be the image of the evaluation map
  [22Xf  ↦  (f(P_1),...,f(P_n))[122X.  The  function  [3XAGCode[103X  computes a list of length
  three,  [G,  n, k], where G is a generator matrix of the AG code C, n is its
  length, and k is its dimension.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XF:=GF(7);;[127X[104X
    [4X[25Xgap>[125X [27XR2:= PolynomialRing( F, 2 );;[127X[104X
    [4X[25Xgap>[125X [27XSetTermOrdering( R2, "lp" );; # --- the term ordering must be "lp"[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing(R2);[127X[104X
    [4X[25Xgap>[125X [27Xindet:= IndeterminatesOfPolynomialRing(R2);;[127X[104X
    [4X[25Xgap>[125X [27Xx:= indet[1];; y:= indet[2];;[127X[104X
    [4X[25Xgap>[125X [27Xf:=x^7-y^2-x;;[127X[104X
    [4X[25Xgap>[125X [27XG:=[2,2,0,0,0,0,0]; D:=[4..8];[127X[104X
    [4X[28X[ 2, 2, 0, 0, 0, 0, 0 ][128X[104X
    [4X[28X[ 4 .. 8 ][128X[104X
    [4X[25Xgap>[125X [27Xagc:=AGCode(f,G,D);[127X[104X
    [4X[28X[ [ [ Z(7)^3, Z(7), 0*Z(7), Z(7)^4, Z(7)^5 ],[128X[104X
    [4X[28X      [ 0*Z(7), Z(7)^4, Z(7)^0, Z(7)^5, Z(7)^3 ],[128X[104X
    [4X[28X      [ 0*Z(7), 0*Z(7), Z(7)^3, Z(7), Z(7)^2 ] ], 5, 3 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThis  generator  matrix  can  be fed into the [5XGUAVA[105X command [2XGeneratorMatCode[102X
  ([14XGUAVA:  GeneratorMatCode[114X) to create a linear code in [5XGAP[105X, which in turn can
  be  fed  into  the [5XGUAVA[105X command [2XMinimumDistance[102X ([14XGUAVA: MinimumDistance[114X) to
  compute the minimum distance of the code.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xag_mat:=agc[1];;[127X[104X
    [4X[25Xgap>[125X [27XC := GeneratorMatCode( ag_mat, GF(7) );[127X[104X
    [4X[28Xa linear [5,3,1..3]2 code defined by generator matrix over GF(7)[128X[104X
    [4X[25Xgap>[125X [27XMinimumDistance(C);[127X[104X
    [4X[28X3[128X[104X
  [4X[32X[104X
  
  
  [1X1.7 [33X[0;0YTroubleshooting and technical stuff[133X[101X
  
  
  [1X1.7-1 [33X[0;0YSupported platforms and underlying [5XGAP[105X[101X[1X functions[133X[101X
  
  [33X[0;0YThis package has been developed mainly on a Linux platform, with [5XGAP[105X version
  4.4,  and  [5XSingular[105X version 2-0-4. A reasonable work has been done to ensure
  backward  compatibility  with  previous versions of [5XGAP[105X 4, but some features
  may  be  missing. This package has been tested also with some other versions
  of  Singular,  including 2-0-3, 2-0-5, and 2-0-6, and on other Unix systems.
  It  has been tested also on Windows, but it is reported to be slower that on
  Linux.[133X
  
  [33X[0;0YThere  is  an  extension of [5XSingular[105X, named [5XPlural[105X, which deals with certain
  noncommutative  polynomial  rings;  see  the [5XSingular[105X documentation, section
  ``7.   PLURAL''.   Currently,   [5XGAP[105X  doesn't  support  these  noncommutative
  polynomial rings. The user of the [5XSingular[105X may use the features of [5XPlural[105X by
  calling the [5XSingular[105X function [3Xncalgebra[103X via [3XSingularInterface[103X. In this case,
  extreme care is needed, because on the [5XGAP[105X side the polynomial will still be
  commutative.[133X
  
  [33X[0;0YFor  the  low-level communication with [5XSingular[105X, the interface relies on the
  [5XGAP[105X  function  [2XInputOutputLocalProcess[102X ([14XReference: InputOutputLocalProcess[114X),
  and  this  function  is  available  only  in  [5XGAP[105X  4.2  (or newer) on a Unix
  environment  or in [5XGAP[105X 4.4 (or newer) on Windows; auto-detection is used. In
  this case, [5XGAP[105X interacts with a unique continuous session of [5XSingular[105X.[133X
  
  [33X[0;0YIn  the case that the [5XGAP[105X function [3XInputOutputLocalProcess[103X is not available,
  then  the  singular  interface will use the [5XGAP[105X function [2XProcess[102X ([14XReference:
  Process[114X).  In  this  case  only a limited subset of the functionality of the
  interface   are   available:   for   example   [2XStartSingular[102X   ([14X1.3-1[114X)   and
  [2XGeneratorsOfInvariantRing[102X  ([14X1.5-7[114X)  are  not  available,  but  [2XGroebnerBasis[102X
  ([14X1.5-1[114X)  is;  [2XSingularInterface[102X  ([14X1.3-8[114X)  supports  less data types. In this
  case, for each function call, a new session of [5XSingular[105X is started and quit.[133X
  
  
  [1X1.7-2 [33X[0;0YHow different versions of [5XGAP[105X[101X[1X display polynomial rings and polynomials[133X[101X
  
  [33X[0;0YThe  way  in which [5XGAP[105X displays polynomials has changed passing from version
  4.3  to  4.4  and the way in which [5XGAP[105X displays polynomial rings has changed
  passing from version 4.4 to 4.5.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X# GAP 4.3 or older[127X[104X
    [4X[25Xgap>[125X [27XR := PolynomialRing( Rationals, [ "x" ] : new );[127X[104X
    [4X[28XPolynomialRing(..., [ x ])[128X[104X
    [4X[25Xgap>[125X [27Xx := IndeterminatesOfPolynomialRing( R )[1];;[127X[104X
    [4X[25Xgap>[125X [27Xx^2 + x;[127X[104X
    [4X[28Xx+x^2[128X[104X
  [4X[32X[104X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X# GAP 4.4[127X[104X
    [4X[25Xgap>[125X [27XR := PolynomialRing( Rationals, [ "x" ] : new );[127X[104X
    [4X[28XPolynomialRing(..., [ x ])[128X[104X
    [4X[25Xgap>[125X [27Xx := IndeterminatesOfPolynomialRing( R )[1];;[127X[104X
    [4X[25Xgap>[125X [27Xx^2 + x;[127X[104X
    [4X[28Xx^2+x[128X[104X
  [4X[32X[104X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X# GAP 4.5 or newer[127X[104X
    [4X[25Xgap>[125X [27XR := PolynomialRing( Rationals, [ "x" ] : new );[127X[104X
    [4X[28XRationals[x][128X[104X
    [4X[25Xgap>[125X [27Xx := IndeterminatesOfPolynomialRing( R )[1];;[127X[104X
    [4X[25Xgap>[125X [27Xx^2 + x;[127X[104X
    [4X[28Xx^2+x[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe examples in this manual use the way of displaying of the newest [5XGAP[105X.[133X
  
  
  [1X1.7-3 [33X[0;0YTest file[133X[101X
  
  [33X[0;0YThe following performs a test of the package functionality using a test file
  [14X'Reference: Test Files'[114X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xfn := Filename( DirectoriesPackageLibrary( "singular", "tst" ), "testall.tst" );;[127X[104X
    [4X[25Xgap>[125X [27XTest( fn );[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  
  [1X1.7-4 [33X[0;0YCommon problems[133X[101X
  
  [33X[0;0YA common error is forgetting to use [2XSingularSetBaseRing[102X ([14X1.3-6[114X). In the next
  example, [3XSingularInterface[103X works only after having used [3XSingularSetBaseRing[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xa:=Indeterminate( Rationals );;[127X[104X
    [4X[25Xgap>[125X [27XF:=AlgebraicExtension( Rationals, a^5+4*a+1 );;[127X[104X
    [4X[25Xgap>[125X [27XR:=PolynomialRing( F, ["x","y"] : old );;[127X[104X
    [4X[25Xgap>[125X [27Xx := R.1;; y := R.2;;[127X[104X
    [4X[25Xgap>[125X [27XSingularInterface( "lead", [x^3*y+x*y+y^2], "poly" );[127X[104X
    [4X[28XError, sorry: Singular, or the interface to Singular, or the current[128X[104X
    [4X[28XSingularBaseRing, do not support the object x^3*y+x*y+y^2.[128X[104X
    [4X[28XDid you remember to use 'SingularSetBaseRing' ?[128X[104X
    [4X[28X[...][128X[104X
    [4X[26Xbrk>[126X [27Xquit;[127X[104X
    [4X[25Xgap>[125X [27XSingularSetBaseRing( R );[127X[104X
    [4X[25Xgap>[125X [27XSingularInterface( "lead", [x^3*y+x*y+y^2], "poly" );[127X[104X
    [4X[28Xx^3*y[128X[104X
  [4X[32X[104X
  
  [33X[0;0YA  corresponding  problem  would  happen  if  the  user  works directly with
  [5XSingular[105X and forgets to define the base-ring at first.[133X
  
  [33X[0;0YAs  explained  in the [5XGAP[105X documentation [14X'Reference: Polynomials and Rational
  Functions'[114X,  given  a  ring  [3XR[103X,  [5XGAP[105X  does  not  consider [3XR[103X as a subset of a
  polynomial  ring  over  [3XR[103X: for example the zero of [3XR[103X ([22X0[122X) and the zero of the
  polynomial  ring  ([22X0x^0[122X)  are  different objects. [5XGAP[105X prints these different
  objects  in the same way, and this fact may be misleading. This is a feature
  of [5XGAP[105X independent from the package [5Xsingular[105X, but it is important to keep it
  in  mind,  as most of the objects used by [5XSingular[105X are polynomials, or their
  coefficients.[133X
  
  
  [1X1.7-5 [33X[0;0YErrors on the [5XSingular[105X[101X[1X side[133X[101X
  
  [33X[0;0YErrors  may occur on the [5XSingular[105X side, for instance using [2XSingularInterface[102X
  ([14X1.3-8[114X)  if  the  arguments  supplied  are  not  appropriate  for the called
  function. In general, it is still an open problem to find a satisfactory way
  to handle in [5XGAP[105X the errors of this kind.[133X
  
  [33X[0;0YAt  the  moment,  when  an  error on the [5XSingular[105X side happens, [5XSingular[105X may
  print an error message on the so-called ``standard error''; this message may
  appear  on  the  screen,  but  it  is  not  logged by the [5XGAP[105X function [2XLogTo[102X
  ([14XReference:  LogTo[114X).  The interface prints [3XNo output from Singular[103X, and then
  the  trivial  object  (of  the  type  specified  as  the  third  argument of
  [3XSingularInterface[103X) may be returned.[133X
  
  
  [1X1.7-6 [33X[0;0YSending a report[133X[101X
  
  [33X[0;0YAs every software, also this package may contain bugs. If you find a bug, or
  a  missing  feature,  or  some  other  problem,  or if you have comments and
  suggestions,  or  if you need some help, you may do so via our issue tracker
  at  [7Xhttps://github.com/gap-packages/singular/issues[107X.  Please  include in the
  report  the  code  that  causes  the  problem,  so that we can replicate the
  problem.[133X
  
  [33X[0;0YIf  appropriate,  you can set [2XInfoSingular[102X ([14X1.7-8[114X) to [3X3[103X, to see what happens
  between  [5XGAP[105X  and  [5XSingular[105X  (but  this may give a lot of output). Note that
  [2XLogTo[102X  ([14XReference:  LogTo[114X)  does  not  log  messages written directly on the
  screen by [5XSingular[105X.[133X
  
  [33X[0;0YEvery  report  about  this  package is welcome, however the probability that
  your  problem  will be fixed quickly increases if you read the text ``How to
  Report                          Bugs                          Effectively'',
  [7Xhttps://www.chiark.greenend.org.uk/~sgtatham/bugs.html[107X  ,  and  send  a  bug
  report according to this text.[133X
  
  [1X1.7-7 SingularReportInformation[101X
  
  [33X[1;0Y[29X[2XSingularReportInformation[102X(  ) [32X function[133X
  
  [33X[0;0YThe function [3XSingularReportInformation[103X collects a description of the system,
  which should be included in any bug report.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSingularReportInformation();[127X[104X
    [4X[28XPkg_Version := "4.04.15";[128X[104X
    [4X[28XGap_Version := "4.dev";[128X[104X
    [4X[28XGap_Architecture := "i686-pc-linux-gnu-gcc";[128X[104X
    [4X[28XGap_BytesPerVariable := 4;[128X[104X
    [4X[28Xuname := "Linux 2.4.20 i686";[128X[104X
    [4X[28XSingular_Version: := 2004;[128X[104X
    [4X[28XSingular_Name: := "/usr/local/Singular/2-0-4/ix86-Linux/Singular";[128X[104X
    [4X[28X[128X[104X
    [4X[28X"Pkg_Version := \"4.04.15\";\nGap_Version := \"4.dev\";\nGap_Architecture := \[128X[104X
    [4X[28X\"i686-pc-linux-gnu-gcc\";\nGap_BytesPerVariable := 4;\nuname := \"Linux 2.4.2\[128X[104X
    [4X[28X0 i686\";\nSingular_Version: := 2004;\nSingular_Name: := \"/usr/local/Singular\[128X[104X
    [4X[28X/2-0-4/ix86-Linux/Singular\";\n"[128X[104X
  [4X[32X[104X
  
  [1X1.7-8 InfoSingular[101X
  
  [33X[1;0Y[29X[2XInfoSingular[102X [32X info class[133X
  
  [33X[0;0YThis is the info class [14X'Reference: Info Functions'[114X used by the interface. It
  can be set to levels 0, 1, 2, and 3. At level 0 no information is printed on
  the  screen.  At  level 1 (default) the interface prints a message about the
  [3Xtype_output[103X,  when  "def"  is  used in [3XSingularInterface[103X, see the example at
  [2XSingularInterface[102X  ([14X1.3-8[114X). At level 2, information on the activities of the
  interface  is printed (e.g., messages when a [5XSingular[105X session, or a Groebner
  basis  calculation,  is  started or terminated). At level 3 all strings that
  [5XGAP[105X  sends  to  [5XSingular[105X  are  printed, as well as all strings that [5XSingular[105X
  sends back.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSetInfoLevel( InfoSingular, 2 );[127X[104X
    [4X[25Xgap>[125X [27XG:= SymmetricGroup( 3 );;[127X[104X
    [4X[25Xgap>[125X [27XR:= PolynomialRing( GF(2), 3 );;[127X[104X
    [4X[25Xgap>[125X [27XGeneratorsOfInvariantRing( R, G );[127X[104X
    [4X[28X#I  running SingularInterface( "invariant_ring", [ "matrix", "matrix"[128X[104X
    [4X[28X ], "list" )...[128X[104X
    [4X[28X#I  done SingularInterface.[128X[104X
    [4X[28X[ x_1+x_2+x_3, x_1*x_2+x_1*x_3+x_2*x_3, x_1*x_2*x_3 ][128X[104X
    [4X[25Xgap>[125X [27XI:= Ideal( R, last );;[127X[104X
    [4X[25Xgap>[125X [27XGroebnerBasis( I );[127X[104X
    [4X[28X#I  running GroebnerBasis...[128X[104X
    [4X[28X#I  done GroebnerBasis.[128X[104X
    [4X[28X[ x_1+x_2+x_3, x_2^2+x_2*x_3+x_3^2, x_3^3 ][128X[104X
    [4X[25Xgap>[125X [27XSetInfoLevel( InfoSingular, 1 );[127X[104X
  [4X[32X[104X
  
