a g c g a b f g X b f a X 2.2 f g X b a a g c f g X b f a X true f g X b f a X true a 0 20654 b 0 3 c 0 1 f 2 0 f 2 1 2 0 g 1 0 a 0 0 g 1 1 20653 a g c g a b f g X b a false a g c false NaTT certifiable-1.6