A Concise Introduction to Logic, Patrick J. Hurley, Wadsworth, 2006, 9th ed,. 7.7, 15, p. 390

 Prove the logical truth.

1.     ~ P v Q 2.     P v ~ Q 3.     P ⊃ Q 4.     ~ Q v P 5.     Q ⊃ P 6.     (P ⊃ Q) • (Q ⊃ P) 7.     P ≡ Q 8.     (P v ~ Q) ⊃ (P ≡ Q) 9.     (~ P v Q) ⊃ [(P v ~ Q) ⊃ (P ≡ Q)]

/ (~ P v Q) ⊃ [(P v ~ Q) ⊃ (P ≡ Q)] ACP ACP 1 Impl 2 Com 4 Impl 3,5 Conj 6 Equiv 2-7 CP 1-8 CP