Checking to see if an element is in a tree in Prolog

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I am trying to write the rules for a predicate in Prolog that will see if a particular member (E) is in a given tree. The tree is not BST, it's like an unsorted binary tree. I can't figure out what is wrong with the logic in the code below.

treeMember(E, node(X, _, _)).
treeMember(E, node(X, L, _)) :- 
    treeMember(E, L).
treeMember(E, node(X, _, R)) :-  
    treeMember(E, R).

The given example query is

?-treeMember(3,node(1, node(2, node(3,nil,nil),node(4,nil,nil)), node(5,nil,nil))).

and that should give a '''true''', which the code does but it'll always give a true even when the (E) in question is not part of the tree. May I please have some pointers?

prolog
1 Answers

It's the first clause when E must be unifiable with X.

treeMember(E, node(E, _, _)) :- !.
treeMember(E, node(_, L, _)) :- 
    L \= nil,
    treeMember(E, L).
treeMember(E, node(_, _, R)) :-  
    R \= nil,
    treeMember(E, R).
user_13104170
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