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