Module ext_invert (subst : ext_subst_sig) <: ext_invert_sig.
Include subst.
Set Bullet Behavior "Strict Subproofs".
Set Implicit Arguments.

Lemma invert_a_Fam : forall G F A,
Typing G (a_Fam F) A ->
exists a B, DefEq G (dom G) A B a_Star /\
binds F (Ax a B) toplevel /\ Typing nil B a_Star.