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