f x f a a f f f f a a a a x 2.2 f x f a a f f f a a a a f x f a a f f a a a f x f a a f f f f a a a a x true f x f a a f f f f a a a a x true 2 1 a 0 1 2 f 2 0 0 1 0 1 0 0 1 0 2 0 1 f 2 1 0 1 0 1 1 0 1 0 2 0 0 f x f a a f f f f a a a a x f x f a a f f a a a false f x f a a f f f a a a a false NaTT certifiable-1.6