∀ {α : Type u} [inst : BEq α] [inst_1 : Hashable α] {β : Type v} {γ : Type w}
  (m : Std.DHashMap.Internal.Raw₀ α fun x => β) [EquivBEq α] [LawfulHashable α] {f : α → β → Option γ} {k k' : α},
  (↑m).WF →
    m.getKey? k = some k' →
      Std.DHashMap.Internal.Raw₀.Const.get? (Std.DHashMap.Internal.Raw₀.filterMap f m) k =
        (Std.DHashMap.Internal.Raw₀.Const.get? m k).bind fun x => f k' x