|  |  3.1.3 The online help system 
The online help system is invoked by the helpcommand.?may be used as a synonym forhelp.  Simply typinghelp;displays the "top" of the help system (i.e., the title
page of the SINGULAR manual) which offers a
short table of contents.  Typinghelptopic;shows the
available documentation on the respective topic.  Here, topic may be either a function
name or, more generally, any index entry of the SINGULAR
manual. Furthermore, topic may contain wildcard characters.
See  help, for more information. 
Online help information can be displayed in various help browsers. The
following table lists a summary of the browsers which are always present.
Usually, external browsers are much more convenient:
A complete, customizable list can be found in the file LIB/help.cnf. 
 
| Browser | Platform | Description |  | html | Windows | displays a html version of the manual in your default html browser |  | builtin | all | simply outputs the help information in plain ASCII format |  | emacs | Unix, Windows | when running SINGULAR within (X)emacs, displays help inside the
(X)emacs info buffer. |  | dummy | all | displays an error message due to the non-availability of a help browser |  
External browsers depend on your system and the contents of LIB/help.cnf,
the default includes:htmlview(displays HTML help pages viahtlmview),
 mac(displays HTML help pages viaopen),
 mac-net(displays HTML help pages viaopen),
 mozilla(displays HTML help pages viamozilla),
 firefox(displays HTML help pages viafirefox),
 konqueror(displays HTML help pages viakonqueror),
 galeon(displays HTML help pages viagaleon),
 netscape(displays HTML help pages vianetscape),
 safari(displays HTML help pages on MacOsX viasafari),
 tkinfo(displays INFO help pages viatkinfo),
 xinfo(displays INFO help pages viainfo),
 info(displays INFO help pages viainfo),
 lynx(displays HTML help pages vialynx). 
The browser which is used to display the help information, can be either
set at startup time with the command line option  (see  Command line options)
or with the SINGULAR command (see  system)
The  SINGULAR command
lists all available browsers and the command
returns the currently used browser. 
If no browser is explicitly set by the user, then the first available browser
(w.r.t. the order of the browsers in the file LIB/help.cnf) is chosen. 
The .singularrc(see  Startup sequence) file is a good place
to set your default browser. Recall that if a file$HOME/.singularrcexists on your system, then the content of this
file is executed before the first user input. Hence, putting in your file|  | if (! system("--emacs"))
{
  // only set help browser if not running within emacs
  system("--browser", "info");
}
// if help browser is later on set to a web browser,
// allow it to fetch HTML pages from the net
system("--allow-net", 1);
 | 
 $HOME/.singularrcsets your default browser toinfo, unless SINGULAR is run within emacs (in which case the
default browser is automatically set toemacs).
Obviously, certain external files and programs are required for the
SINGULAR help system to work correctly. If something is not available
or goes wrong, here are some tips for troubleshooting the help system:
 
 
Under Unix, the environment variable DISPLAYhas to be set for all X11
browsers to work.
The help browsers are only available if the respective programs are installed
on your system (for xinfo, the programsxtermandinfoare necessary). You can explicitly specify which program to
use, by changing the entry inLIB/help.cnf
If the help browser cannot find the local html
pages of the SINGULAR manual (which it will look for at
$RootDir/html-- see  Loading a library for more info on$RootDir) and the (command-line) option--allow-nethas explicitly been set (see  Command line options and
 system for more info on
setting values of command-line options), then it dispatches the html
pages from
https://www.singular.uni-kl.de/Manual. (Note that
the non-local net-access of HTML pages is disabled, by default.)An
alternative location of a local directory where the html pages reside
can be specified by setting the environment variable
 SINGULAR_HTML_DIR.
The infobased help browserstkinfo,xinfo,info, andbuiltinneed the (info) filesingular.hlpwhich will be looked
for at$RootDir/info/singular.hlp(see  Loading a library
for more info on$RootDir).  An alternative
location of the info file of the manual can be specified by setting the
environment variableSINGULAR_INFO_FILE. 
 Command line options
 
  Info help browsers 
The help browsers tkinfo,xinfoandinfo(so-called
info help browsers) are based on theinfoprogram from the GNUtexinfopackage.  See section `Getting started' in The Info Manual, for more
information. 
For info help browsers, the online manual is decomposed into "nodes"
of information, closely
related to the division of the printed manual into sections and
subsections.  A node contains text describing a specific topic at a
specific level of detail.  The top line of a node is its "header".
The node's header tells the name of the current node (Node:), the
name of the next node (Next:), the name of the previous node
(Prev:), and the name of the upper node (Up:). 
To move within info, type commands consisting of single characters.  Do
not type RETURN.  Do not use cursor keys, either.  Using some of
the cursor keys by accident might pop to some totally different node.
Typelto return to the original node.  Some of theinfocommands read input from the command line at the bottom.  TheTABkey may be used to complete partially entered input. 
The most important commands are:
 
qleaves the online help system
ngoes to the next node
pgoes to the previous node
ugoes to the upper node
mpicks a menu item specified by name
ffollows a cross reference
lgoes to the previously visited node
bgoes to the beginning of the current node
egoes to the end of the current node
SPACEscrolls forward a page
DELscrolls backward a page
hinvokes info tutorial (use lto return to the manual orCTRL-X 0to remove extra window)CTRL-Hshows a short overview over the online help system (use lto return
to the manual orCTRL-X 0to remove extra window)ssearches through the manual for a specific string, and selects the node in
which the next occurrence is found
1, ...,9picks i-th subtopic from a menu
 
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