Program Fixpoint find_x (a: elt) {wf (order uf.(m)) a} :
    { r: elt * t | fst r = repr uf a /\ forall x, repr (snd r) x = repr uf x } :=
  match M.get a uf.(m) with
  | Some a' =>
      match find_x a' with
      | pair b uf' => (b, compress uf' a b _ _)
      end
  | None => (a, uf)
  end.Definition find (a: elt) : elt * t := proj1_sig (find_x a).

Lemma find_repr: forall a, fst (find a) = repr uf a.