On 3rd and 4th moments of finite upper half plane graphs

Families of Ramanujan graphs and quaternion algebras

“…To the best of our knowledge this question is open. See [39] for some discussion of this and [21] for the failure of the "naive conjecture". 5.3.…”

On character sums with distances on the upper half plane over a finite field

“…For various structural properties of H q , interested readers can see the series of papers [2,3,9,16,19,20] and references therein. In particular, they naturally lead to new examples of Ramanujan graphs (see [5,10,[12][13][14]).…”