∀ {α : Type u} {cmp : α → α → Ordering} {β : Type v} {t₁ t₂ : Std.DTreeMap α (fun x => β) cmp} [Std.TransCmp cmp]
  [inst : Inhabited (α × β)] {k : α},
  t₁.Equiv t₂ → Std.DTreeMap.Const.getEntryLT! t₁ k = Std.DTreeMap.Const.getEntryLT! t₂ k