Module unique := fc_unique wf subst.

Lemma erase_cpi : forall AB0 A B G S, erase AB0 = (a_CPi A B) -> AnnTyping G AB0 S -> exists A1 B0, erase AB0 = erase (a_CPi A1 B0) /\ erase_constraint A1 = A /\ erase B0 = B /\ AnnTyping G (a_CPi A1 B0) a_Star.