“…This constituted the first concrete example of an attack on the exceptional components of type 4. This was then finally generalized in [19], where an algorithm, called the DAFC, is given to compute an 'approximate' fundamental domain, and hence generators, for subgroups of finite index in groups that are contained in the unit group of orders in quaternion algebras over Q or quadratic imaginary extensions of Q, in particular for Bianchi groups. This work handled the exceptional components of type 1 and 2, as well as a part of exceptional components of type 4.…”