X is removed from OldList, resultin in NewList. List3 is the concatenation of List1 and List2. Newlist is the result of removing the first occurrence of Item from List. Fails when Item is not member of List.
List is a list of elements that are currently uninstantiated or instantiated to an atom or number.
Composes a complex Term with functor Symbol and arguments ArgList. Unify Term1 with Term2 including occurs check. Unify the complex terms Term1 and Term2. Result is the result of substituting occurrences of Term for each free occurrence of Variable in Exp. N is the current Skolem function index.