TRS: { del(.(x, .(y, z))) -> f(=(x, y), x, y, z), f(true(), x, y, z) -> del(.(y, z)), f(false(), x, y, z) -> .(x, del(.(y, z))), =(nil(), nil()) -> true(), =(.(x, y), nil()) -> false(), =(nil(), .(y, z)) -> false(), =(.(x, y), .(u(), v())) -> and(=(x, u()), =(y, v()))} Fail