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