f a h x f g x h x h g x h a g h x g x h h x x 2.2 g h x g x f a h x f g x h x h g x h a f a h x g x true h g x h a false f a h x f g x h x true h 1 1 1 a 0 28959 f 2 0 h 1 0 f 2 1 0 g 1 0 g 1 28958 g h x g x f a h x g x false g h x g x true h 1 1 1 a 0 28959 f 2 0 h 1 0 f 2 1 0 g 1 1 0 g 1 8856 g h x g x NaTT certifiable-1.6