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