MAYBE MAYBE TRS: { mark(__(X1, X2)) -> active(__(mark(X1), mark(X2))), mark(nil()) -> active(nil()), mark(and(X1, X2)) -> active(and(mark(X1), X2)), mark(tt()) -> active(tt()), mark(isNePal(X)) -> active(isNePal(mark(X))), __(X1, mark(X2)) -> __(X1, X2), __(X1, active(X2)) -> __(X1, X2), __(mark(X1), X2) -> __(X1, X2), __(active(X1), X2) -> __(X1, X2), active(__(X, nil())) -> mark(X), active(__(__(X, Y), Z)) -> mark(__(X, __(Y, Z))), active(__(nil(), X)) -> mark(X), active(and(tt(), X)) -> mark(X), active(isNePal(__(I, __(P, I)))) -> mark(tt()), and(X1, mark(X2)) -> and(X1, X2), and(X1, active(X2)) -> and(X1, X2), and(mark(X1), X2) -> and(X1, X2), and(active(X1), X2) -> and(X1, X2), isNePal(mark(X)) -> isNePal(X), isNePal(active(X)) -> isNePal(X) } DUP: We consider a non-duplicating system. Trs: { mark(__(X1, X2)) -> active(__(mark(X1), mark(X2))), mark(nil()) -> active(nil()), mark(and(X1, X2)) -> active(and(mark(X1), X2)), mark(tt()) -> active(tt()), mark(isNePal(X)) -> active(isNePal(mark(X))), __(X1, mark(X2)) -> __(X1, X2), __(X1, active(X2)) -> __(X1, X2), __(mark(X1), X2) -> __(X1, X2), __(active(X1), X2) -> __(X1, X2), active(__(X, nil())) -> mark(X), active(__(__(X, Y), Z)) -> mark(__(X, __(Y, Z))), active(__(nil(), X)) -> mark(X), active(and(tt(), X)) -> mark(X), active(isNePal(__(I, __(P, I)))) -> mark(tt()), and(X1, mark(X2)) -> and(X1, X2), and(X1, active(X2)) -> and(X1, X2), and(mark(X1), X2) -> and(X1, X2), and(active(X1), X2) -> and(X1, X2), isNePal(mark(X)) -> isNePal(X), isNePal(active(X)) -> isNePal(X) } Fail