Two-Generator Discrete and Faithful Subgroups of Tree Automorphisms

Abstract

We present a partial classification of two-generator discrete and faithful subgroups of the trivalent tree automorphism group, specifically for cases where the generators satisfy a restriction on a small geometric quantity. When the restrictions on the geometric quantity or tree valency are relaxed, we discuss the possible reduced quotient graphs for these subgroups and construct infinite families of graphs of groups on each. Additionally, we include a generalized Poincaré algorithm that determines whether a given set of tree automorphisms generates a discrete subgroup.