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