∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.DTreeMap.Raw α β cmp} [Std.TransCmp cmp]
  [Std.LawfulEqCmp cmp] [inst : Inhabited α],
  t.WF → t.isEmpty = false → ∀ {km : α}, t.minKey! = km ↔ km ∈ t ∧ ∀ k ∈ t, (cmp km k).isLE = true