∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [inst : BEq α]
  [Std.TransOrd α] [Std.LawfulBEqOrd α],
  t.WF →
    ∀ {k : α} {v : β},
      (Std.DTreeMap.Internal.Impl.Const.toArray (Std.DTreeMap.Internal.Impl.insert! k v t)).Perm
        ((Array.filter (fun x => decide ¬(k == x.1) = true) (Std.DTreeMap.Internal.Impl.Const.toArray t)).push (k, v))