Systoles of arithmetic surfaces and the Markoff spectrum.
The arithmetic hyperbolic 3-manifold of smallest volume
The congruence subgroup problem for algebraic groups
The connection between quadratic forms and the extended modular group
In this paper some properties of quadratic forms whose base points lie in the point set , the fundamental domain of the modular group, and transforming these forms into the reduced forms with the same discriminant are given.
The connections between continued fraction representations of units and certain Hecke groups.
The covolume of quaternion groups on the four-dimensional hyperbolic space
The determination of parabolic points in modular and extended modular groups by continued fractions.
The Farey graph.
The finite subgroups of maximal arithmetic kleinian groups
Given a maximal arithmetic Kleinian group , we compute its finite subgroups in terms of the arithmetic data associated to by Borel. This has applications to the study of arithmetic hyperbolic 3-manifolds.
The geometry and spectrum of the one holed torus.
The Modular Torus has Maximal Length Spectrum.
The √p Riemann surface
The Schur Multiplicator of SL(2, Z/mZ) and the Congruence Subgroup Property.
The Selberg trace formula for the Picard group SL(2, Z[i])
Theta Series on the Hecke Groups G(...2) and G(...3).
Über eine arithmetische Aufspaltung der logarithmischen Ableitung Selbergscher Zetafunktionen
Über explizite Präsentationen Hilbertscher Modulgruppen zu totalrellen Körpern der Klassenzahlen eins.
Über Tschebyscheff-Polynome, Nicht-Kongruenzuntergruppen der Modulgruppe und Fibonacci-Zahlen.
Über vollständige Automorphismengruppen und Gleichungen in der Modulgruppe
Ueber ausgezeichnete Untergruppen in der Gruppe der elliptischen Modulfunctionen