On the Covering Problem for Left-Recursive Grammars

Abstract Two new proofs of the fact that proper left-recursive grammars can be covered by non-left-recursive grammars are presented. The first proof is based on a simple trick inspired by the over ten-year-old idea that semantic information hanged on the productions can be carried along in the transformations. The second proof involves a new method for eliminating left recursion from a proper context-free grammar in such a way that the covering grammar is obtained directly.