f a f x a f a f f f a a a x 2.2 f a f x a f f f a a a x f a f x a f f a a a f a f x a f a f f f a a a x f a f x a f a a true f a f x a f a f f f a a a x true 2 1 a 0 1 6390 f 2 0 0 1 0 1 0 0 1 0 2 0 6389 f 2 1 1 1 0 2 0 0 f a f x a f a f f f a a a x f a f x a f a a false f a f x a f f a a a false f a f x a f f f a a a x false NaTT certifiable-1.6