The maximal discrete extension of SL2(O-K) for an imaginary quadratic number field K

摘要

Let OK be the ring of integers of an imaginary quadratic number field K. In this paper we give a new description of the maximal discrete extension of the group SL2(OK) inside SL2(C), which uses generalized Atkin-Lehner involutions. Moreover we find a natural characterization of this group in SO(1, 3).