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