∀ {X : Type u_1} [t : TopologicalSpace X] {C D : Set X} [inst : Topology.RelCWComplex C D]
  (E : Topology.RelCWComplex.Subcomplex C) (F : Set X),
  F = ↑E →
    ∀ (J : (n : ℕ) → Set (Topology.RelCWComplex.cell C n)),
      J = E.I → D ∪ ⋃ n, ⋃ j, Topology.RelCWComplex.openCell n ↑j = F