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