In the limit, going down to one dimensions, the full apeirogonal group is obtained when the angle goes to zero, so [∞], abstractly the infinite dihedral group D ∞, represents two parallel mirrors and has a Coxeter diagram . The apeirogonal group [∞], , abstractly the infinite cyclic group Z ∞, isomorphic to the additive group of the integers, is generated by a single nonzero translation.