∀ {E : Type u_1} [inst : TopologicalSpace E] {G : Type u_3} [inst_1 : AddGroup G] [inst_2 : AddAction G E]
  [ContinuousConstVAdd G E] [ProperlyDiscontinuousVAdd G E] [LocallyCompactSpace E] [T2Space E],
  IsCoveringMapOn (Quotient.mk (AddAction.orbitRel G E))
    (Quotient.mk (AddAction.orbitRel G E) '' {e | AddAction.stabilizer G e = ⊥})