Prove that [4x)A(x)]' → (Vx)[A(x)]' is valid. We must prove the implication in each direction. a. [ax)4(x)]' <→ (Vx)[A(x)]' The hypothesis alone gives us little to work with, so we introduce a (somewhat surprising) temporary hypothesis. A proof sequence is 1. [Ex)A(x)]' 2. A(x) 3. (Ex)A(x) hyp temporary hyp 2, eg 4. A(x) → (Ax)A(x) temporary hyp discharged 5. [A(x)]' 1, 4, mt 6. (Vx)[A(x)]' 5, ug b. (Vx)[4(x)]' → [x)A(x)]' This proof also requires a temporary hypothesis. It is even more surprising than case (a) because we assume the exact opposite of the conclusion we are trying to reach. 1. (Vx)[A(x)]' 2. (Ex)4(x) hyp temporary hyp 3. A(a) 2, ei 4. [A(a)]' 1, ui 5. [(Vx)[A(x)]'I' 6. (Ax)A(x) → [(Vx)[A(x)]]' temporary hyp discharged 3, 4, inc 7. [((Vx)[A(x)])]' 1, dn 8. [Ex)4(x)]' 6, 7, mt
Prove that [4x)A(x)]' → (Vx)[A(x)]' is valid. We must prove the implication in each direction. a. [ax)4(x)]' <→ (Vx)[A(x)]' The hypothesis alone gives us little to work with, so we introduce a (somewhat surprising) temporary hypothesis. A proof sequence is 1. [Ex)A(x)]' 2. A(x) 3. (Ex)A(x) hyp temporary hyp 2, eg 4. A(x) → (Ax)A(x) temporary hyp discharged 5. [A(x)]' 1, 4, mt 6. (Vx)[A(x)]' 5, ug b. (Vx)[4(x)]' → [x)A(x)]' This proof also requires a temporary hypothesis. It is even more surprising than case (a) because we assume the exact opposite of the conclusion we are trying to reach. 1. (Vx)[A(x)]' 2. (Ex)4(x) hyp temporary hyp 3. A(a) 2, ei 4. [A(a)]' 1, ui 5. [(Vx)[A(x)]'I' 6. (Ax)A(x) → [(Vx)[A(x)]]' temporary hyp discharged 3, 4, inc 7. [((Vx)[A(x)])]' 1, dn 8. [Ex)4(x)]' 6, 7, mt
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
Related questions
Question
Prove that
[(∀x)A(x)]′ ↔ (∃x)[A(x)]′
is valid.
![Prove that
[4x)A(x)]' → (Vx)[A(x)]'
is valid. We must prove the implication in each direction.
a. [ax)4(x)]' <→ (Vx)[A(x)]'
The hypothesis alone gives us little to work with, so we introduce a (somewhat
surprising) temporary hypothesis. A proof sequence is
1. [Ex)A(x)]'
2. A(x)
3. (Ex)A(x)
hyp
temporary hyp
2, eg
4. A(x) → (Ax)A(x) temporary hyp discharged
5. [A(x)]'
1, 4, mt
6. (Vx)[A(x)]'
5, ug
b. (Vx)[4(x)]' → [x)A(x)]'
This proof also requires a temporary hypothesis. It is even more surprising than
case (a) because we assume the exact opposite of the conclusion we are trying to
reach.
1. (Vx)[A(x)]'
2. (Ex)4(x)
hyp
temporary hyp
3. A(a)
2, ei
4. [A(a)]'
1, ui
5. [(Vx)[A(x)]'I'
6. (Ax)A(x) → [(Vx)[A(x)]]' temporary hyp discharged
3, 4, inc
7. [((Vx)[A(x)])]'
1, dn
8. [Ex)4(x)]'
6, 7, mt](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F6ba6f0aa-4586-4d51-bf6a-64967a8f1492%2Fa216c4de-bee3-4eab-a51c-7b2c4ad9e5d0%2Fe05aia5.png&w=3840&q=75)
Transcribed Image Text:Prove that
[4x)A(x)]' → (Vx)[A(x)]'
is valid. We must prove the implication in each direction.
a. [ax)4(x)]' <→ (Vx)[A(x)]'
The hypothesis alone gives us little to work with, so we introduce a (somewhat
surprising) temporary hypothesis. A proof sequence is
1. [Ex)A(x)]'
2. A(x)
3. (Ex)A(x)
hyp
temporary hyp
2, eg
4. A(x) → (Ax)A(x) temporary hyp discharged
5. [A(x)]'
1, 4, mt
6. (Vx)[A(x)]'
5, ug
b. (Vx)[4(x)]' → [x)A(x)]'
This proof also requires a temporary hypothesis. It is even more surprising than
case (a) because we assume the exact opposite of the conclusion we are trying to
reach.
1. (Vx)[A(x)]'
2. (Ex)4(x)
hyp
temporary hyp
3. A(a)
2, ei
4. [A(a)]'
1, ui
5. [(Vx)[A(x)]'I'
6. (Ax)A(x) → [(Vx)[A(x)]]' temporary hyp discharged
3, 4, inc
7. [((Vx)[A(x)])]'
1, dn
8. [Ex)4(x)]'
6, 7, mt
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