Some extreme discrete groups

Abstract

TROELS JORCENSEN and IIIAIRE KIIKKA Let' X and y be two Mbius transformations generating a non- elementary discrete group. A lemma in 12] then tells us that (*) where X and Y are thoughtof ascomplexunimodulat 2-by-2 matrices (and X-1 and Y-L as the inverse matrices) and z denotes the trace function.