f f a f x a a f a f f x a a 2.2 f f a f x a a f f x a a f f a f x a a f a f f x a a true f f a f x a a f f x a a true a 0 1 f 2 1 2 21238 f 2 1 0 f f a f x a a f a f f x a a f f a f x a a f a f f x a a false NaTT certifiable-1.6