Alexander Meduna Martin Svec Descriptional Complexity of Generalized Forbidding Grammars. 11-17 2003 80 Int. J. Comput. Math. 1 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0020-7160&volume=80&issue=1&spage=11 db/journals/ijcm/ijcm80.html#MedunaS03