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