?- help(term_expansion/2).

?- help(term_expansion/2).
term_expansion(+Term1, -Term2)
    Dynamic  and  multifile  predicate,  normally  not defined.     When
    defined  by the user all terms  read during consulting are given  to
    this predicate.   If the predicate succeeds Prolog will assert Term2
    in  the database rather than the read term (Term1).  Term2  may be a
    term  of the form ?- Goal.  or :- Goal.   Goal is then treated as  a
    directive.   If Term2  is a list, all  terms of the list are  stored
    in  the database or  called (for directives).   If  Term2 is of  the
    form  below, the system will assert Clause and record  the indicated
    source location with it:

         '$source_location'(<File>, <Line>):<Clause>

    When compiling a  module (see chapter 6 and the directive module/2),
    expand_term/2  will first try  term_expansion/2 in the module  being
    compiled  to  allow  for term  expansion  rules  that are  local  to
    a  module.     If  there  is  no  local  definition,  or  the  local
    definition  fails  to translate  the  term,  expand_term/2 will  try
    term_expansion/2  in module user.    For compatibility with  SICStus
    and  Quintus Prolog,  this feature  should not  be used.   See  also
    expand_term/2, goal_expansion/2 and expand_goal/2.

true.