See the library package check for example usage. Head is a term whose name and arity are identical to the predicate. Unify FileName with the name of the sourcefile in which the predicate is defined. Unify LineNumber with the line number of the first clause of the predicate. Fails if the predicate is not associated with a file.
Term is a term, which name and arity are used as a predicate specification.
What I Mean' sence. Backtracking provides all alternative matches. Succeeds when Head can be unified with a clause head and Body with the corresponding clause body. Gives alternative clauses on backtracking. For facts Body is unified with the atom true .