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