ref: fa83d3f1aba932e99833244ebb38b7415b142bd7
dir: /stdlib.pl/
% Logic and control predicates \+ Goal :- call(Goal), !, fail. \+ Goal. once(Goal) :- call(Goal), !. repeat :- true ; repeat. % Control structures. true. If -> Then :- If, !, Then. If -> Then ; _ :- If, !, Then. _ -> _ ; Else :- !, Else. If ; _ :- If. _ ; Else :- Else. % Term unification A = A. A \= B :- \+ A = B. % Comparison of terms using the standard order A == B :- compare(=, A, B). A \== B :- \+ A == B. A @< B :- compare(<, A, B). A @=< B :- A == B. A @=< B :- A @< B. A @> B :- compare(>, A, B). A @>= B :- A == B. A @>= B :- A @> B.