∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [Std.TransOrd α] (h : t.WF)
  {k : α} {f : Option β → Option β},
  (Std.DTreeMap.Internal.Impl.Const.alter k f t ⋯).impl.isEmpty = false →
    ∀ {fallback : α},
      (Std.DTreeMap.Internal.Impl.Const.alter k f t ⋯).impl.minKeyD fallback = k ↔
        (f (Std.DTreeMap.Internal.Impl.Const.get? t k)).isSome = true ∧ ∀ k' ∈ t, (compare k k').isLE = true