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