@inproceedings{Sti_j2003_a, Author = {Ralf~Stiebe}, Title = {Positive valence grammars}, Editor = {Erzs\'ebet~Csuhaj-Varj\'u and Chandra~M.~R.~Kintala and Detlef~Wotschke and Gy{\"o}rgy~Vaszil}, Booktitle = {Descriptional Complexity of Formal Systems}, Publisher = {MTA SZTAKI}, Address = {Budapest}, Year = 2003, Pages = {186--197} }