∀ {α : Type u} {β : α → Type v} {m : Std.DHashMap.Raw α β} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α]
  [LawfulHashable α],
  m.WF →
    ∀ {k a fallback : α} {v : β k},
      (m.insertIfNew k v).getKeyD a fallback = if (k == a) = true ∧ k ∉ m then k else m.getKeyD a fallback