two different approaches of defining 'member' predicate

[sovereig...@outlook.com]

case1

member(X,[X|R]).

member(X,[Y|R]) :- member(X,R).

case2

member(X,[_|R]) :- member(X,R).

member(X,[X|_]).

Is there any chance that two approaches would produce different prolog goal beavior? 

[Feliks Kluzniak]

Yes, for example, if the second argument is an uninstantiated variable.  In case 2 you will immediately go into endless recursion.

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