p-Torsion in the class group of curves with too many automorphisms

citation_journal_title=C. R. Acad. Sci. Paris; citation_title=Une Nouvelle Opération sur les Formes Différentielles; citation_author=P. Cartier; citation_volume=244; citation_publication_date=1957; citation_pages=426-428; citation_id=CR1 C.Chevalley, Introduction to the Theory of Algebraic Functions of One Variable. New York 1951. citation_journal_title=Monatsh. Math. Phys.; citation_title=Zyklische unverzweigte Erweiterungskörper vom Primzahlgradep über einem algebraischen Funktionenkörper der Charakteristikp ; citation_author=H. Hasse, E. Witt; citation_volume=43; citation_publication_date=1936; citation_pages=477-493; citation_id=CR3 citation_journal_title=Amer. Math. Soc. Transl.; citation_title=The Hasse-Witt matrix of an Algebraic Curve; citation_author=Ju. Manin; citation_volume=45; citation_publication_date=1965; citation_pages=245-264; citation_id=CR4 citation_journal_title=Invent. Math.; citation_title=Subvarieties of Moduli Spaces; citation_author=F. Oort; citation_volume=24; citation_publication_date=1974; citation_pages=95-119; citation_id=CR5 J.-P.Serre, Sur la topologie des variétés algébriques en caractéristiquep. Dans: Sympos. Internac. Topol. Alg., Mexico City 1956, pp. 24–53. citation_journal_title=Arch. Math.; citation_title=Über die Automorphismengruppe eines algebraischen Funktionenkörpers von Primzahlcharakteristik, Teil I; citation_author=H. Stichtenoth; citation_volume=24; citation_publication_date=1973; citation_pages=527-544; citation_id=CR7 citation_journal_title=Arch. Math.; citation_title=Über die Automorphismengruppe eines algebraischen Funktionenkörpers von Primzahlcharakteristik, Teil II; citation_author=H. Stichtenoth; citation_volume=24; citation_publication_date=1973; citation_pages=615-631; citation_id=CR8 F.Sullivan, Thep-division Points of the Jacobian Variety of ap-cyclic Extension ofk(x). To appear in Rend. Sem. Mat. Univ. Padova.