(VAR X X1 X2 Y )
(RULES 
        active(from(X)) -> mark(cons(X, from(s(X))))
        active(length(nil)) -> mark(0)
        active(length(cons(X, Y))) -> mark(s(length1(Y)))
        active(length1(X)) -> mark(length(X))
        mark(from(X)) -> active(from(mark(X)))
        mark(cons(X1, X2)) -> active(cons(mark(X1), X2))
        mark(s(X)) -> active(s(mark(X)))
        mark(length(X)) -> active(length(X))
        mark(nil) -> active(nil)
        mark(0) -> active(0)
        mark(length1(X)) -> active(length1(X))
        from(mark(X)) -> from(X)
        from(active(X)) -> from(X)
        cons(mark(X1), X2) -> cons(X1, X2)
        cons(X1, mark(X2)) -> cons(X1, X2)
        cons(active(X1), X2) -> cons(X1, X2)
        cons(X1, active(X2)) -> cons(X1, X2)
        s(mark(X)) -> s(X)
        s(active(X)) -> s(X)
        length(mark(X)) -> length(X)
        length(active(X)) -> length(X)
        length1(mark(X)) -> length1(X)
        length1(active(X)) -> length1(X)
        
)