We consider the question of existence of ramified covers over P_1 matching certain prescribed ramification conditions. This problem has already been faced in a number of papers, but we discuss alternative approaches for an existence proof, involving elliptic curves and universal ramified covers with signature. We also relate the geometric problem with finite permutation groups and with the Fermat-Euler Theorem on the representation of a prime as a sum of two squares.
On certain permutation groups and sums of two squares / Corvaja, P; Petronio, Carlo; Zannier, U.. - In: ELEMENTE DER MATHEMATIK. - ISSN 0013-6018. - 67:(2012), pp. 169-181. [10.4171/EM/207]
On certain permutation groups and sums of two squares
PETRONIO, CARLO;
2012-01-01
Abstract
We consider the question of existence of ramified covers over P_1 matching certain prescribed ramification conditions. This problem has already been faced in a number of papers, but we discuss alternative approaches for an existence proof, involving elliptic curves and universal ramified covers with signature. We also relate the geometric problem with finite permutation groups and with the Fermat-Euler Theorem on the representation of a prime as a sum of two squares.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
