Hint Extern 1 (lc_co (g_AbsCong _ _ _)) =>
  let x1 := fresh in
  pick_fresh x1;
  apply (lc_g_AbsCong_exists x1).Hint Extern 1 (lc_co (g_CAbsCong _ _ _)) =>
  let c1 := fresh in
  pick_fresh c1;
  apply (lc_g_CAbsCong_exists c1).

Lemma tm_subst_tm_tm_degree_tm_wrt_co : forall a1 a2 x1 n1, degree_tm_wrt_co n1 a1 -> degree_tm_wrt_co n1 a2 -> degree_tm_wrt_co n1 (tm_subst_tm_tm a2 x1 a1).