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