@ARTICLE{DasPau_j1990_b, author = {J{\"u}rgen~Dassow and Gheorghe~P\u{a}un}, title = {On the degree of non-regularity of context-free languages}, journal = ijcm, year = 1990, volume = 36, number = {}, pages = {13--29}, url = {http://dx.doi.org/10.1080/00207169008803907} }