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Each of Exercises \(20-32\) asks you to show that two compound propositions are logically equivalent. To do this, either show that both sides are true, or that both sides are false, for exactly the same combinations of truth values of the propositional variables in these expressions (whichever is easier). Show that \(\neg p \rightarrow(q \rightarrow r)\) and \(q \rightarrow(p \vee r)\) are logically equivalent.

Short Answer

Expert verified
They are logically equivalent as both expressions have the same truth values for all combinations of \(p\), \(q\), and \(r\).

Step by step solution

01

Write the expressions

Start by writing down the two compound propositions that need to be shown as logically equivalent:1. \(eg p \rightarrow (q \rightarrow r)\)2. \(q \rightarrow (p \vee r)\)
02

Determine truth values for all variables

Create a truth table with all possible truth value combinations for the variables \(p\), \(q\), and \(r\).
03

Fill in the initial truth values

Construct rows in the truth table for \(p\), \(q\), and \(r\) with all possible combinations:\[\{ (T, T, T), (T, T, F), (T, F, T), (T, F, F), (F, T, T), (F, T, F), (F, F, T), (F, F, F) \}\]
04

Calculate intermediate values

Compute the values for the intermediate logical expressions step-by-step:1. Get \(eg p\) for each combination.2. Get \(q \rightarrow r \).3. Get \(eg p \rightarrow (q \rightarrow r)\).
05

Calculate \(eg p \rightarrow (q \rightarrow r)\)

Evaluate the logical implication \(eg p \rightarrow (q \rightarrow r)\) for each row in the truth table.
06

Calculate \(q \rightarrow (p \vee r)\)

Evaluate the logical implication \(q \rightarrow (p \vee r)\) for each row in the truth table.
07

Compare the final columns

Compare the truth values of \(eg p \rightarrow (q \rightarrow r)\) and \(q \rightarrow (p \vee r)\) in the final columns to confirm logical equivalence. If the truth values match for all combinations, then the two propositions are logically equivalent.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

truth table
A truth table is a mathematical table used to determine if a compound proposition is true or false. It lists all possible truth values for the propositional variables and shows the resulting truth values for the compound propositions.

In our exercise, we consider three variables: \(p\), \(q\), and \(r\). We begin by listing all possible combinations of these variables, which are 8 such combinations for truth values (True or False):
\[ \begin{array}{cccc} p & q & r \ \hline T & T & T \ T & T & F \ T & F & T \ T & F & F \ F & T & T \ F & T & F \ F & F & T \ F & F & F \end{array} \].

This table allows us to evaluate the logical propositions for each combination of truth values, providing a clear method to verify logical equivalence.
compound propositions
A compound proposition consists of two or more simpler propositions connected by logical connectors such as AND (\(\land \)), OR (\(\lor \)), NOT (\(eg \)), and IMPLICATION (\(\rightarrow\) ). For example, \( eg p \rightarrow (q \rightarrow r)\) and \( q \rightarrow (p \vee r)\) are compound propositions.

In the given problem, we need to show that these two compound propositions are logically equivalent. We do this by evaluating the truth values of these propositions for all possible combinations of \(p\), \(q\), and \(r\).

By using a truth table, we systematically break down the propositions and evaluate their truth values step-by-step. This approach can simplify complex logical expressions and help illustrate the relationships between different propositions.
logical implication
Logical implication is a type of logical connective typically represented as \(\rightarrow\). It expresses a conditional relationship between two propositions. The statement \(A \rightarrow B\) means 'if A is true, then B must also be true.'

Importantly, \(A \rightarrow B\) is true in all cases except when A is true and B is false.

In our problem, we analyze expressions like \( eg p \rightarrow (q \rightarrow r) \) and \( q \rightarrow (p \vee r) \). To demonstrate logical equivalence, we must show that both implications yield the same truth values across all combinations of \(p\), \(q\), and \(r\). This involves calculating intermediate values precisely using the rules of logical implication.

In essence, checking logical implications through truth tables helps in visualizing how the truth values of compound propositions relate.
propositional variables
Propositional variables are the fundamental building blocks in propositional logic, representing individual statements that can either be true (T) or false (F). The variables \(p\), \(q\), and \(r\) in our problem each stand for some proposition with a truth value.

A statement like \(p\) could represent a simple declarative statement (e.g., 'It is raining'), while complex propositions would combine these variables in various logical forms (AND, OR, NOT).

In our task, we use propositional variables to create truth tables. Each combination of these variables helps us evaluate the overall truth value of compound propositions.

By systematically examining all possible truth values of \(p\), \(q\), and \(r\), we can effectively demonstrate logical equivalence between complex logical expressions. This methodical approach ensures a comprehensive understanding of how various logical connections affect the truth of propositions.

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Most popular questions from this chapter

Express the negation of each of these statements in terms of quantifiers without using the negation symbol. a) \(\forall x(x>1)\) b) \(\forall x(x \leq 2)\) \(\begin{array}{ll}\text { c) } & \exists x(x \geq 4)\end{array}\) d) \(\exists x(x<0)\) e) \(\forall x((x<-1) \vee(x>2))\) f) \(\exists x((x<4) \vee(x>7))\)

Translate in two ways each of these statements into logical expressions using predicates, quantifiers, and logical connectives. First, let the domain consist of the students in your class and second, let it consist of all people. a) Someone in your class can speak Hindi. b) Everyone in your class is friendly. c) There is a person in your class who was not born in California. d) A student in your class has been in a movie. e) No student in your class has taken a course in logic programming.

Express the negation of these propositions using quantifiers, and then express the negation in English. a) Some drivers do not obey the speed limit. b) All Swedish movies are serious. c) No one can keep a secret. d) There is someone in this class who does not have a good attitude.

Exercises \(61-64\) are based on questions found in the book Symbolic Logic by Lewis Carroll. Let P(x), Q(x), and R(x) be the statements 鈥渪 is a clear explanation,鈥 鈥渪 is satisfactory,鈥 and 鈥渪 is an excuse,鈥 respectively. Suppose that the domain for x consists of all English text. Express each of these statements using quantifiers, logical connectives, and P(x), Q(x), and R(x). a) All clear explanations are satisfactory. b) Some excuses are unsatisfactory. c) Some excuses are not clear explanations. d) Does (c) follow from (a) and (b)?

Exercises \(40-44\) deal with the translation between system specification and logical expressions involving quantifiers. Translate these specifications into English, where \(F(p)\) is "printer \(p\) is out of service," \(B(p)\) is "Printer \(p\) is busy," \(L(j)\) is "Print job \(j\) is lost, " and \(Q(j)\) is "Print job \(j\) is queued." $$ \begin{array}{l}{\text { a) } \exists p(F(p) \wedge B(p)) \rightarrow \exists j L(j)} \\ {\text { b) } \forall p B(p) \rightarrow \exists j Q(j)} \\\ {\text { c) } \exists j(Q(j) \wedge L(j)) \rightarrow \exists p F(p)} \\\ {\text { d) }(\forall p B(p) \wedge \forall j Q(j)) \rightarrow \exists j L(j)}\end{array} $$

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