f a f x a f f a f f a a x a 2.2 f a f x a f a f f a a x f a f x a f f a a x f a f x a f f a f f a a x a f a f x a f a a true f a f x a f a f f a a x true 2 1 a 0 1 2 f 2 0 0 1 0 1 0 0 1 0 2 23068 1 f 2 1 0 0 0 2 0 0 f a f x a f f a f f a a x a f a f x a f f a f f a a x a false f a f x a f f a a x false f a f x a f a a false NaTT certifiable-1.6