Let be a nonelementary discrete subgroup of . We show that if the sum of diagonal entries of each element of is a complex number, then is conjugate to a subgroup of .
"A characterization of quaternionic Kleinian groups in dimension $2$ with complex trace fields." Algebr. Geom. Topol. 18 (2) 957 - 974, 2018. https://doi.org/10.2140/agt.2018.18.957