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 lc_body_tm_wrt_tm : forall a1 a2, body_tm_wrt_tm a1 -> lc_tm a2 -> lc_tm (open_tm_wrt_tm a1 a2).