Lower bounds for context-free grammars
Ellul, Krawetz, Shallit and Wang prove an exponential lower bound on the size of any context-free grammar generating the language of all permutations over some alphabet. We generalize their method and obtain exponential lower bounds for many other languages, among them the set of all squares of given length, and the set of all words containing each symbol at most twice. (C) 2011 Elsevier B.V. All rights reserved.
lower bounds context-free grammars formal languages