∀ {B : Type u_2} {F : Type u_3} {inst : TopologicalSpace B} {inst_1 : TopologicalSpace F} {E : B → Type u_5}
  {inst_2 : TopologicalSpace (Bundle.TotalSpace F E)} {inst_3 : (b : B) → TopologicalSpace (E b)}
  [self : FiberBundle F E] (b : B), b ∈ (FiberBundle.trivializationAt' b).baseSet