We define a logical connective as follows: P Q is true when both P and Q are false, and it is false otherwise. (We read P↓Q as “P nor Q"). (a) Write a truth table for P Q and check that P Q is logically equivalent to -(PV Q). (b) Check that P+Q=Q↓ P. That is, ↓ is commutative. (e) Show that (PQ) ↓ R and P↓ (QR) are logically inequivalent. That is, is not associative.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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1. We define a logical connective ↓ as follows: \( P \downarrow Q \) is true when both \( P \) and \( Q \) are false, and it is false otherwise. (We read \( P \downarrow Q \) as "P nor Q").

   (a) Write a truth table for \( P \downarrow Q \) and check that \( P \downarrow Q \) is logically equivalent to \( \neg(P \vee Q) \).

   (b) Check that \( P \downarrow Q \equiv Q \downarrow P \). That is, ↓ is commutative.

   (c) Show that \( (P \downarrow Q) \downarrow R \) and \( P \downarrow (Q \downarrow R) \) are logically inequivalent. That is, ↓ is not associative.

   (d) Show that the logical connectives ¬, ∧, and ∨ can each be expressed entirely in terms of ↓, without using any other logical connectives. Specifically, prove the following:
   
      i. \( \neg P \equiv (P \downarrow P) \).
      
      ii. \( P \land Q \equiv (P \downarrow P) \downarrow (Q \downarrow Q) \).
      
      iii. \( P \lor Q \equiv (P \downarrow Q) \downarrow (P \downarrow Q) \).

   (e) Prove that the logical connective ⇒ can be expressed entirely in terms of ↓. That is, show that the sentence \( P \Rightarrow Q \) is logically equivalent to a sentence involving ↓ and no other logical connectives.

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**Explanations of Points:**

- **Truth Table (Point a)**: The task involves creating a table with columns for \( P \), \( Q \), \( P \downarrow Q \), and \( \neg(P \vee Q) \), showing values for all combinations of \( P \) and \( Q \) being true or false. By comparing, it confirms whether \( P \downarrow Q \) is logically equivalent to \( \neg(P \vee Q) \).

- **Commutativity (Point b)**: The goal is to show that swapping \( P \) and \( Q \) in \( P \down
Transcribed Image Text:Here is a transcription of the image along with explanations: --- 1. We define a logical connective ↓ as follows: \( P \downarrow Q \) is true when both \( P \) and \( Q \) are false, and it is false otherwise. (We read \( P \downarrow Q \) as "P nor Q"). (a) Write a truth table for \( P \downarrow Q \) and check that \( P \downarrow Q \) is logically equivalent to \( \neg(P \vee Q) \). (b) Check that \( P \downarrow Q \equiv Q \downarrow P \). That is, ↓ is commutative. (c) Show that \( (P \downarrow Q) \downarrow R \) and \( P \downarrow (Q \downarrow R) \) are logically inequivalent. That is, ↓ is not associative. (d) Show that the logical connectives ¬, ∧, and ∨ can each be expressed entirely in terms of ↓, without using any other logical connectives. Specifically, prove the following: i. \( \neg P \equiv (P \downarrow P) \). ii. \( P \land Q \equiv (P \downarrow P) \downarrow (Q \downarrow Q) \). iii. \( P \lor Q \equiv (P \downarrow Q) \downarrow (P \downarrow Q) \). (e) Prove that the logical connective ⇒ can be expressed entirely in terms of ↓. That is, show that the sentence \( P \Rightarrow Q \) is logically equivalent to a sentence involving ↓ and no other logical connectives. --- **Explanations of Points:** - **Truth Table (Point a)**: The task involves creating a table with columns for \( P \), \( Q \), \( P \downarrow Q \), and \( \neg(P \vee Q) \), showing values for all combinations of \( P \) and \( Q \) being true or false. By comparing, it confirms whether \( P \downarrow Q \) is logically equivalent to \( \neg(P \vee Q) \). - **Commutativity (Point b)**: The goal is to show that swapping \( P \) and \( Q \) in \( P \down
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