MAYBE MAYBE TRS: { top(sent(x)) -> top(check(rest(x))), check(rest(x)) -> rest(check(x)), check(sent(x)) -> sent(check(x)), check(cons(x, y)) -> cons(x, y), check(cons(x, y)) -> cons(x, check(y)), check(cons(x, y)) -> cons(check(x), y), rest(nil()) -> sent(nil()), rest(cons(x, y)) -> sent(y) } DUP: We consider a non-duplicating system. Trs: { top(sent(x)) -> top(check(rest(x))), check(rest(x)) -> rest(check(x)), check(sent(x)) -> sent(check(x)), check(cons(x, y)) -> cons(x, y), check(cons(x, y)) -> cons(x, check(y)), check(cons(x, y)) -> cons(check(x), y), rest(nil()) -> sent(nil()), rest(cons(x, y)) -> sent(y) } Fail