1. Coleman R.F.: Torsion points on Abelian étale coverings of $${{\mathbb P}^{1}-\{0, 1, \infty \}}$$ . Trans. Amer. Math. Soc. 311, 185–208 (1989)
2. E.-U. Gekeler, Cuspidal divisor class groups of modular curves, Algebraic number theory and Diophantine analysis (Graz, 1998), de Gruyter, Berlin, 163–189 (2000).
3. Greenberg R.: On the Jacobian variety of some algebraic curves. Compositio Math. 42, 345–359 (1981)
4. Gross D., Rohrlich B.: Some results on the Mordell-Weil group of the Jacobian of the Fermat curve. Invent. Math. 44, 201–224 (1978)
5. D. Kubert and S. Lang, Modular units, Grundlehren der Mathematischen Wissenschaften 244, Springer-Verlag (1981).