MAYBE

Problem:
 active(nats()) -> mark(adx(zeros()))
 active(zeros()) -> mark(cons(0(),zeros()))
 active(incr(cons(X,Y))) -> mark(cons(s(X),incr(Y)))
 active(adx(cons(X,Y))) -> mark(incr(cons(X,adx(Y))))
 active(hd(cons(X,Y))) -> mark(X)
 active(tl(cons(X,Y))) -> mark(Y)
 mark(nats()) -> active(nats())
 mark(adx(X)) -> active(adx(mark(X)))
 mark(zeros()) -> active(zeros())
 mark(cons(X1,X2)) -> active(cons(X1,X2))
 mark(0()) -> active(0())
 mark(incr(X)) -> active(incr(mark(X)))
 mark(s(X)) -> active(s(X))
 mark(hd(X)) -> active(hd(mark(X)))
 mark(tl(X)) -> active(tl(mark(X)))
 adx(mark(X)) -> adx(X)
 adx(active(X)) -> adx(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)
 incr(mark(X)) -> incr(X)
 incr(active(X)) -> incr(X)
 s(mark(X)) -> s(X)
 s(active(X)) -> s(X)
 hd(mark(X)) -> hd(X)
 hd(active(X)) -> hd(X)
 tl(mark(X)) -> tl(X)
 tl(active(X)) -> tl(X)

Proof:
 Open