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listprologmember

Prolog member/2 predicate

Why does prolog answer false to: member([5], [2, 5]).?

Is there a way to work around it?

Any help will be greatly appreciated.

Solution

  • As described in the SWI Prolog documentation for member/2:

    member(?Elem, ?List )

    True if Elem is a member of List.

    The predicate is member. It is not subset or sublist or subsequence. It succeeds if the first argument is a member (that is, an element) of the list given in the second argument. The element [5] is not a member of the list [2, 5] since the element [5] isn't 2 and it isn't 5. However, [5] would be a member of the list [2, [5]], so member([5], [2, [5]]) would succeed.