a b x1 x1 a c x1 c c x1 b c x1 a a b b x1 2.2 b c x1 a b b x1 b c x1 b b x1 b c x1 a a b b x1 b c x1 b x1 true b c x1 b x1 b c x1 b b x1 true Failed! NaTT certifiable-1.6