Basic theorems about faig-equiv.
Theorem:
(defthm aig-equiv-implies-faig-equiv-cons-1 (implies (aig-equiv a a-equiv) (faig-equiv (cons a b) (cons a-equiv b))) :rule-classes (:congruence))
Theorem:
(defthm aig-equiv-implies-faig-equiv-cons-2 (implies (aig-equiv b b-equiv) (faig-equiv (cons a b) (cons a b-equiv))) :rule-classes (:congruence))