∀ {G : Type u_1} {X : Type u_2} [inst : TopologicalSpace G] [inst_1 : TopologicalSpace X] [inst_2 : Group G]
  [IsTopologicalGroup G] [inst_4 : MulAction G X] [SigmaCompactSpace G] [BaireSpace X] [T2Space X] [ContinuousSMul G X]
  [MulAction.IsPretransitive G X] (x : X), IsOpenMap fun g => g • x