MAYBE Trs: { filter(mark(X1), X2, X3) -> filter(X1, X2, X3), filter(active(X1), X2, X3) -> filter(X1, X2, X3), filter(X1, mark(X2), X3) -> filter(X1, X2, X3), filter(X1, active(X2), X3) -> filter(X1, X2, X3), filter(X1, X2, mark(X3)) -> filter(X1, X2, X3), filter(X1, X2, active(X3)) -> filter(X1, X2, X3), cons(mark(X1), X2) -> cons(X1, X2), cons(active(X1), X2) -> cons(X1, X2), cons(X1, mark(X2)) -> cons(X1, X2), cons(X1, active(X2)) -> cons(X1, X2), s(mark(X)) -> s(X), s(active(X)) -> s(X), sieve(mark(X)) -> sieve(X), sieve(active(X)) -> sieve(X), mark(0()) -> active(0()), mark(zprimes()) -> active(zprimes()), mark(filter(X1, X2, X3)) -> active(filter(mark(X1), mark(X2), mark(X3))), mark(cons(X1, X2)) -> active(cons(mark(X1), X2)), mark(s(X)) -> active(s(mark(X))), mark(sieve(X)) -> active(sieve(mark(X))), mark(nats(X)) -> active(nats(mark(X))), active(zprimes()) -> mark(sieve(nats(s(s(0()))))), active(filter(cons(X, Y), 0(), M)) -> mark(cons(0(), filter(Y, M, M))), active(filter(cons(X, Y), s(N), M)) -> mark(cons(X, filter(Y, N, M))), active(sieve(cons(0(), Y))) -> mark(cons(0(), sieve(Y))), active(sieve(cons(s(N), Y))) -> mark(cons(s(N), sieve(filter(Y, N, N)))), active(nats(N)) -> mark(cons(N, nats(s(N)))), nats(mark(X)) -> nats(X), nats(active(X)) -> nats(X)} Comment: We consider a duplicating trs. FAIL: Open