simple induction 1.
intros.
inversion_clear H2; trivial with arith pts.
simple destruct v; intros.
inversion_clear H2.
inversion_clear H3; auto with arith pts.
Qed.

Lemma sub_decl_eq_def :
forall (m t T : term) (n : nat) (g e f : env),
sub_in_env g (Def m T) t n e f -> t = m.