f 0 1 x f s x x x f x y s z s f 0 1 z 2.2 f 0 1 x f s x x x f x y s z f 0 1 z true f x y s z f 0 1 z f 0 1 x f s x x x true 1 0 1 s 1 1 1 f 3 0 0 0 1 f 3 3 0 f 0 1 x f s x x x f 0 1 x f s x x x false NaTT certifiable-1.6