End ext_subst_sig.
(**************** Ext invert ****************)
Module Type ext_invert_sig.
Include ext_subst_sig.
(* ---------- inversion lemmas ---------------- *)

Axiom invert_a_Var :
forall G x A, Typing G (a_Var_f x) A -> exists A', binds x (Tm A') G /\ DefEq G (dom G) A A' a_Star.