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