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