A b x1 b a B A x1 B a x1 a b A B x1 A a x1 x1 B b x1 x1 2.2 B a x1 B x1 A b x1 B A x1 B a x1 A B x1 A b x1 A x1 true A b x1 A x1 B a x1 A B x1 A b x1 B A x1 B a x1 B x1 true Failed! NaTT certifiable-1.6