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