A Concise Introduction to Logic, Patrick J. Hurley, Wadsworth, 2006, 9th ed,. 8.7, III, 5 p. 448

The author of King Lear was an English actor. John Milton was English but not an actor. Therefore, John Milton is not the author of King Lear. (Wxy: x wrote y; Ex: x is English; Ax: x is an actor; k: King Lear; m: John Milton)

1.     (∃x)[Wxk • (y)(Wyk ⊃ y= x) • Ax • Ex] 2.     Em • ~ Am ∴ ~ Wmk 3.     Wrk • (y)(Wyk ⊃ y= r) • Ar • Er 4.     (y)(Wyk ⊃ y= r) • Ar • Er • Wrk 5.     (y)(Wyk ⊃ y= r) 6.     Wmk ⊃ m= r 7.     ~ ~ Wmk 8.     Wmk 9.     m = r 10. Ar • (y)(Wyk ⊃ y= r) • Er • Wrk 11. Ar 12. ~ Am • Em 13. ~ Am 14. Am 15. Am • ~ Am 16. ~ ~ ~ Wmk 17. ~ Wmk

1 EI 3 Com 4 Simp 5 UI AIP 7 DN 6,8 MP 4 Com 10 Simp 2 Com 12 Simp 9,11 Id 13,14 Conj 7-15 IP 16 DN