A Concise Introduction to Logic, Patrick J. Hurley, Wadsworth, 2006, 9th ed,. 7.7, 20, p. 390

 Prove the logical truth.

1.     P 2.     Q • P 3.     Q 4.     (Q • P) ⊃ Q 5.     Q ⊃ (P ⊃ Q) 6.     P ⊃ Q 7.     Q 8.     (P ⊃ Q) ⊃ Q 9.     [Q ⊃ (P ⊃ Q)] • [(P ⊃ Q) ⊃ Q] 10.  Q ≡ (P ⊃ Q) 11.  P ⊃ [Q ≡ (P ⊃ Q)]

/ P ⊃ [Q ≡ (P ⊃ Q)] ACP ACP 2 Simp 1-4 CP 4 Exp ACP 1,6 MP 6-7 CP 5,8 Conj 9 Equiv 1,10 CP