This module provides help/1 and apropos/1 that give help on a topic or searches the manual for relevant topics.
By default the result of help/1 
is sent through a pager such as
less. This behaviour is controlled by the following:
help_pager, which can be set to one of 
the following values:
PAGER or otherwise tries 
to find the less program.
program_name(Arg, ...). 
For example, less('-r') would be the default. Note that the 
program name can be an absolute path if single quotes are used.
topics(s) to give help for. Notations for What 
are:
?- help(append).
/ Arity// ArityIf an exact match fails this predicates attempts fuzzy matching and, when successful, display the results headed by a warning that the matches are based on fuzzy matching.
If possible, the results are sent through a pager such as the
less program. This behaviour is controlled by the Prolog 
flag
help_pager. See section level documentation.
:Textsection, cfunction, function,
iso_predicate, swi_builtin_predicate, library_predicate,
dcg and aliases chapter, arithmetic, c_function,
predicate, nonterminal and non_terminal. 
For example:
?- apropos(c:close). ?- apropos(f:min).
The library(explain) describes prolog-terms. The most 
useful functionality is its cross-referencing function.
?- explain(subset(_,_)).
"subset(_, _)" is a compound term
        Referenced from 2-th clause of lists:subset/2
        Referenced from 46-th clause of prolog_xref:imported/3
        Referenced from 68-th clause of prolog_xref:imported/3
lists:subset/2 is a predicate defined in
        /staff/jan/lib/pl-5.6.17/library/lists.pl:307
        Referenced from 2-th clause of lists:subset/2
        Possibly referenced from 2-th clause of lists:subset/2
Note that the help-tool for XPCE provides a nice graphical cross-referencer.
Name/Arity 
or a term of the form Module:Name/Arity, explain/1 
describes the predicate as well as possible references to it. See also gxref/0.