Module ext_subst (weak : ext_weak_sig) <: ext_subst_sig.
Include weak.
induction G2; [ | inversion 1]; simpl; auto.
Qed.

Lemma binds_map_4: forall x A F c0,
binds x (Tm A) F ->
binds x (Tm (co_subst_co_tm g_Triv c0 A)) (map (co_subst_co_sort g_Triv c0) F).