Iwan M. Duursma Bjorn Poonen Michael Zieve Everywhere Ramified Towers of Global Function Fields. 148-153 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2948&spage=148 2003 conf/fq/2003 International Conference on Finite Fields and Applications db/conf/fq/fq2003.html#DuursmaPZ03