% complex_structure(ID, some random list of stuff)
complex_structure(1, [1, 2, 3]).
complex_structure(2, [3, 2, 1]).

unique_structure_broken(X, Y) :-
    X = complex_structure(A1, _),
    Y = complex_structure(A2, _),
        call(X),call(Y),
        A1\=A2,
    X \= Y.

unique_structure(X, Y) :-
    complex_structure(1, X),
    complex_structure(2, Y),
    X \= Y.