Free Groups in Quaternion Algebras

S. O. Juriaans, A. C. Souza Filho

In \cite{jpsf} we constructed pairs of units $u,v$ in $\mathbb{Z}$-orders of a quaternion algebra over $\Q (\sqrt{-d})$, $d\equiv 7(\mathrm{mod}8)$ positive and square free, such that $< u^ n,v^…