weird_sum(List, Sum) :-
    weird_sum(List, 0, Sum).

weird_sum([], Acc, Sum) :- Sum is Acc.
weird_sum([X|Xs], Sum0, Sum) :-
    once( weird_sum_helper(X, Sum0, Sum1) ),
    weird_sum(Xs, Sum1, Sum).

weird_sum_helper(X, Acc, Acc + X*X) :- X >= 5.
weird_sum_helper(X, Acc, Acc - X) :- X =< 2.
weird_sum_helper(X, Acc, Acc) :- X < 5, X > 2.