∀ {V : Type u_1} {M : Type u_2} [inst : Group M] [inst_1 : MulAction M V] {S : Type u_3} (ι : S → M)
  (x : Quiver.SchreierGraph V ι) (a : Quiver.Costar x),
  (Quiver.SchreierGraph.labellingCostarEquiv ι x) a = (Quiver.SchreierGraph.labelling V ι).costar x a