f f x a a f f f x a f a a a 2.2 f f x a a f f x a f a a f f x a a f a a f f x a a f f f x a f a a a true f f x a a f f f x a f a a a false f f x a a f a a false f f x a a f f x a f a a false NaTT certifiable-1.6