(VAR L X X1 X2 )
(RULES 
        active(incr(nil)) -> mark(nil)
        active(incr(cons(X, L))) -> mark(cons(s(X), incr(L)))
        active(adx(nil)) -> mark(nil)
        active(adx(cons(X, L))) -> mark(incr(cons(X, adx(L))))
        active(nats) -> mark(adx(zeros))
        active(zeros) -> mark(cons(0, zeros))
        active(head(cons(X, L))) -> mark(X)
        active(tail(cons(X, L))) -> mark(L)
        mark(incr(X)) -> active(incr(mark(X)))
        mark(nil) -> active(nil)
        mark(cons(X1, X2)) -> active(cons(mark(X1), X2))
        mark(s(X)) -> active(s(mark(X)))
        mark(adx(X)) -> active(adx(mark(X)))
        mark(nats) -> active(nats)
        mark(zeros) -> active(zeros)
        mark(0) -> active(0)
        mark(head(X)) -> active(head(mark(X)))
        mark(tail(X)) -> active(tail(mark(X)))
        incr(mark(X)) -> incr(X)
        incr(active(X)) -> incr(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)
        adx(mark(X)) -> adx(X)
        adx(active(X)) -> adx(X)
        head(mark(X)) -> head(X)
        head(active(X)) -> head(X)
        tail(mark(X)) -> tail(X)
        tail(active(X)) -> tail(X)
        
)