Forbidding ET0L grammars

AbstractThe present paper introduces and discusses forbidding ET0L grammars whose productions have some attached strings, called forbidding conditions. These grammars can make a derivation step only by using productions whose forbidding conditions do not appear in the rewritten sentential form. The paper demonstrates that some well-known relationships concerning the language families resulting from ordinary ET0L grammars do not hold in terms of the forbidding ET0L grammars. Most interestingly, while E0L grammars are less powerful than ET0L grammars, their forbidding versions with conditions of length one are equally powerful. On the other hand, while EP0L grammars are as powerful as E0L grammars, FEP0L grammars are less powerful than FE0L grammars