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