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