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