Thursday, 8 April 2021

A Concise Introduction to Logic, Patrick J. Hurley, Wadsworth, 2006, 9th ed,. 8.7, III, 15 p. 449

Every candidate except Mary was elected. The only candidate who was elected was Ralph. Mary is not Ralph. Therefore, there were exactly two candidates. (Cx: x is a candidate; Ex: x was elected; m: Mary; r: Ralph)

1.     Cm • ~ Em • (x)[(Cx • x ≠ m) ⊃ Ex]

2.     Cr • Er • (x)[(Cx • Ex) ⊃ x = r]

3.     ≠ r

∴ (∃x)(∃y){Cx • Cy • x  ≠  y • (z)[Cz ⊃ (z = x v z = y)]}

4.     ~ (∃x)(∃y){Cx • Cy • x  ≠  y • (z)[Cz ⊃ (z = x v z = y)]}

5.     (x)(y)~{Cx • Cy • x  ≠  y • (z)[Cz ⊃ (z = x v z = y)]}

6.     (x)(y){~(Cx • Cy • x  ≠  y) v ~(z)[Cz ⊃ (z = x v z = y)]}

7.     (x)(y){~(Cx • Cy • x  ≠  y) v (z)~[Cz ⊃ (z = x v z = y)]}

8.     (x)(y){~(Cx • Cy • x  ≠  y) v (z)~[~Cz v (z = x v z = y)]}

9.     (x)(y){~(Cx • Cy • x  ≠  y) v (z)[Cz • (z = x v z = y)]}

10.  (x)(y)[~(Cx • Cy • x  ≠  y) v (z)(Cz • z  x  z  y)]

11.  (y)[~(Cm • Cy • m  ≠  y) v (z)(Cz • z  m  z  y)]

12.  ~(Cm • Cr • m  ≠  r) v (z)(Cz • z  m  z  r)

13.  Cm

14.  Cr

15.  Cm • Cr • m  ≠  r

16.  (z)(Cz • z  m  z  r)

17.  Cq • q  m  q  r

18.  (x)[(Cx • x ≠ m) ⊃ Ex] • Cm • ~ Em

19.  (x)[(Cx • x ≠ m) ⊃ Ex]

20.  (Cq • q ≠ m) ⊃ Eq

21.  Cq • q  m

22.  Eq

23.  (x)[(Cx • Ex) ⊃ x = r]  Cr • Er

24.  (x)[(Cx • Ex) ⊃ x = r]

25.  (Cq • Eq) ⊃ q = r

26.  Cq

27.  Cq • Eq

28.  q = r

29.   r • Cq • q  m

30.   r

31.  q = r  q  r

32.  ~ ~ (∃x)(∃y){Cx • Cy • x  ≠  y • (z)[Cz ⊃ (z = x v z = y)]}

33.  (∃x)(∃y){Cx • Cy • x  ≠  y • (z)[Cz ⊃ (z = x v z = y)]}

 

 

 

 

AIP

4 QC

5 DM

6 QC

7 Impl

8 DM

9 DM

10 UI

11 UI

1 Simp

2 Simp

3,13,14 Conj

12,15 DS.

16 EI

1 Com

18 Simp

19 UI

17 Simp

20,21 MP

2 Com

23 Simp

24 UI

21 Simp

22,26 Conj

25,27 MP

17 Com

29 Simp

28,30 Conj

4-31 IP

32 DN

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