∀ {α : Type u} {β : α → Type v} (m : Std.DHashMap.Internal.Raw₀ α β) [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α]
  [LawfulHashable α] {f : α → Bool} {k fallback : α},
  (↑m).WF →
    (Std.DHashMap.Internal.Raw₀.filter (fun k x => f k) m).getKeyD k fallback =
      (Option.filter f (m.getKey? k)).getD fallback