b a b c c b x1 a b b c c b a x1 2.2 b a b c c b x1 b c c b a x1 b a b c c b x1 b a x1 b a b c c b x1 b b c c b a x1 true b a b c c b x1 b a x1 true a 1 1 1 b 1 1 1 c 1 1 0 b 1 1 0 b a b c c b x1 b b c c b a x1 false b a b c c b x1 b c c b a x1 false NaTT certifiable-1.6