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% 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.
A , B :- A , B.
% 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.
% List predicates
length([], 0).
length([_|Tail], Length) :-
length(Tail, Length0),
Length is Length0 + 1.
member(X, [X|_]).
member(X, [_|Tail]) :-
member(X, Tail).
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