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