∀ {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], (↑m).WF → ∀ {a fallback : α}, m.contains a = true → m.getKey? a = some (m.getKeyD a fallback)