MAYBE

Problem:
 active(nats()) -> mark(cons(0(),incr(nats())))
 active(pairs()) -> mark(cons(0(),incr(odds())))
 active(odds()) -> mark(incr(pairs()))
 active(incr(cons(X,XS))) -> mark(cons(s(X),incr(XS)))
 active(head(cons(X,XS))) -> mark(X)
 active(tail(cons(X,XS))) -> mark(XS)
 mark(nats()) -> active(nats())
 mark(cons(X1,X2)) -> active(cons(mark(X1),X2))
 mark(0()) -> active(0())
 mark(incr(X)) -> active(incr(mark(X)))
 mark(pairs()) -> active(pairs())
 mark(odds()) -> active(odds())
 mark(s(X)) -> active(s(mark(X)))
 mark(head(X)) -> active(head(mark(X)))
 mark(tail(X)) -> active(tail(mark(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)
 head(mark(X)) -> head(X)
 head(active(X)) -> head(X)
 tail(mark(X)) -> tail(X)
 tail(active(X)) -> tail(X)

Proof:
 Open