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