Section A.
Variable a : nat.
Variable b : nat.
Variable c : nat.
Variable H1 : a = 3.
Variable H2 : a = 3 -> b = 7.
Variable H3 : c = 3.
Proof using Type*.
pose H1 as e1.
pose H2 as e2.
reflexivity.
Qed.
Proof using b*.
exact H2.
Qed.

Lemma baz : c=3.