f a f x a f a f f a a x 2.2 f a f x a f f a a x f a f x a f a a f a f x a f a f f a a x true f a f x a f a f f a a x true 2 1 a 0 1 20539 f 2 0 0 1 0 1 0 0 1 0 2 15921 1 f 2 2 0 0 f a f x a f a f f a a x f a f x a f a a false f a f x a f f a a x false NaTT certifiable-1.6