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