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