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