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