@Article{DasSti_j2008, author = {J{\"u}rgen~Dassow and Ralf~Stiebe}, title = {Nonterminal Complexity of Some Operations on Context-Free Languages}, journal = fundinform, year = {2008}, volume = 83, number = {1--2}, pages = {35--49}, url = {http://iospress.metapress.com/content/926763k0718q0252/fulltext.pdf} } %http://fi.mimuw.edu.pl/abs83.html#4