∀ {X : Type u_1} [t : TopologicalSpace X] {C D : Set X} [inst : T2Space X] [inst_1 : Topology.RelCWComplex C D] {n : ℕ∞}
  {m : ℕ} {j : Topology.RelCWComplex.cell C m},
  n ≤ ↑m →
    ↑(Topology.RelCWComplex.skeletonLT C n) ∩ Topology.RelCWComplex.closedCell m j =
      ↑(Topology.RelCWComplex.skeletonLT C n) ∩ Topology.RelCWComplex.cellFrontier m j