MAYBE MAYBE TRS: { sieve(X) -> n__sieve(X), sieve(cons(X, Y)) -> cons(X, n__filter(X, n__sieve(activate(Y)))), from(X) -> cons(X, n__from(n__s(X))), from(X) -> n__from(X), s(X) -> n__s(X), primes() -> sieve(from(s(s(0())))), cons(X1, X2) -> n__cons(X1, X2), head(cons(X, Y)) -> X, activate(X) -> X, activate(n__from(X)) -> from(activate(X)), activate(n__s(X)) -> s(activate(X)), activate(n__filter(X1, X2)) -> filter(activate(X1), activate(X2)), activate(n__cons(X1, X2)) -> cons(activate(X1), X2), activate(n__sieve(X)) -> sieve(activate(X)), tail(cons(X, Y)) -> activate(Y), if(true(), X, Y) -> activate(X), if(false(), X, Y) -> activate(Y), filter(X1, X2) -> n__filter(X1, X2), filter(s(s(X)), cons(Y, Z)) -> if( divides(s(s(X)), Y), n__filter(n__s(n__s(X)), activate(Z)), n__cons(Y, n__filter(X, n__sieve(Y))) ) } DUP: We consider a duplicating system. Trs: { sieve(X) -> n__sieve(X), sieve(cons(X, Y)) -> cons(X, n__filter(X, n__sieve(activate(Y)))), from(X) -> cons(X, n__from(n__s(X))), from(X) -> n__from(X), s(X) -> n__s(X), primes() -> sieve(from(s(s(0())))), cons(X1, X2) -> n__cons(X1, X2), head(cons(X, Y)) -> X, activate(X) -> X, activate(n__from(X)) -> from(activate(X)), activate(n__s(X)) -> s(activate(X)), activate(n__filter(X1, X2)) -> filter(activate(X1), activate(X2)), activate(n__cons(X1, X2)) -> cons(activate(X1), X2), activate(n__sieve(X)) -> sieve(activate(X)), tail(cons(X, Y)) -> activate(Y), if(true(), X, Y) -> activate(X), if(false(), X, Y) -> activate(Y), filter(X1, X2) -> n__filter(X1, X2), filter(s(s(X)), cons(Y, Z)) -> if( divides(s(s(X)), Y), n__filter(n__s(n__s(X)), activate(Z)), n__cons(Y, n__filter(X, n__sieve(Y))) ) } Fail