f a f a x f a f f a x f a a 2.2 f a f a x f f a x f a a f a f a x f a a f a f a x f a f f a x f a a true f a f a x f a f f a x f a a f a f a x f f a x f a a true a 0 3 f 2 2 f 2 1 0 f a f a x f a f f a x f a a f a f a x f a f f a x f a a f a f a x f a f f a x f a a true 2 1 a 0 1 2 f 2 0 0 1 0 1 840 1 f 2 1 1 1 1 2 0 0 f a f a x f a f f a x f a a f a f a x f a a false NaTT certifiable-1.6