PPT Slide

mem2(2,[1,2,3])

/*A*/ mem2(X,[_|T]) :- mem2(X,T)./*B*/ mem2(X,[X|_]).

How Prolog Proceeds - 1

Matches A,

Unify [_|T]

with [1,2,3]

So T = [2,3],

and must prove

mem2(X,T).