Require Export FcEtt.imports.
Require Export FcEtt.fset_facts.
Require Export FcEtt.ett_inf.
Require Export FcEtt.ett_ind.
Require Export FcEtt.beta.
Require Export FcEtt.ext_wf.
Require Export FcEtt.ett_value.
Set Bullet Behavior "Strict Subproofs".
Set Implicit Arguments.
Module ext_subst (weak : ext_weak_sig) <: ext_subst_sig.
Include weak.

Lemma Ctx_strengthen : forall G1 G2, Ctx (G2 ++ G1) -> Ctx G1.
induction G2; [ | inversion 1]; simpl; auto.