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