(VAR X X1 X2 Y Z )
(RULES 
        fst(0, Z) -> nil
        fst(s(X), cons(Y, Z)) -> cons(Y, n__fst(activate(X), activate(Z)))
        from(X) -> cons(X, n__from(n__s(X)))
        add(0, X) -> X
        add(s(X), Y) -> s(n__add(activate(X), Y))
        len(nil) -> 0
        len(cons(X, Z)) -> s(n__len(activate(Z)))
        fst(X1, X2) -> n__fst(X1, X2)
        from(X) -> n__from(X)
        s(X) -> n__s(X)
        add(X1, X2) -> n__add(X1, X2)
        len(X) -> n__len(X)
        activate(n__fst(X1, X2)) -> fst(activate(X1), activate(X2))
        activate(n__from(X)) -> from(activate(X))
        activate(n__s(X)) -> s(X)
        activate(n__add(X1, X2)) -> add(activate(X1), activate(X2))
        activate(n__len(X)) -> len(activate(X))
        activate(X) -> X
        
)