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