Resumen de The minimum index of a non-congruence subgroup of SL2 over an arithmetic domain. II: the rank zero cases

A. W. Mason, Andreas Schweizer

• Let be a function field of genus with a finite constant field . Choose a place of of degree and let be the arithmetic Dedekind domain consisting of all elements of that are integral outside . An explicit formula is given (in terms of , and ) for the minimum index of a non-congruence subgroup in SL. It turns out that this index is always equal to the minimum index of an arbitrary proper subgroup in SL. The minimum index of a normal non-congruence subgroup is also determined.