∀ {α : Type u_1} {β : Type u_2} [inst : Ord α] [Std.TransOrd α] (k : α) (size : ℕ) (ky : α) (y : β)
  (l r : Std.DTreeMap.Internal.Impl α fun x => β),
  (∃ a ∈ Std.DTreeMap.Internal.Impl.inner size ky y l r, compare a k = Ordering.lt) →
    ¬compare k ky = Ordering.gt → ∃ a ∈ l, compare a k = Ordering.lt