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Determine whether \((\neg q \wedge(p \rightarrow q)) \rightarrow \neg p\) is a tautology.

Short Answer

Expert verified
Yes, it is a tautology.

Step by step solution

01

- Understand the Problem

A tautology is a formula that is true for all possible truth values of its variables. The given logical expression is \((eg q \wedge (p \rightarrow q)) \rightarrow eg p \). We need to determine if this expression is always true.
02

- Rewrite the Implication

Recall that an implication \(A \rightarrow B\) is equivalent to \(eg A \vee B\). Therefore, rewrite the expression \((p \rightarrow q)\) as \(eg p \vee q\). The expression now looks like this: \((eg q \wedge (eg p \vee q)) \rightarrow eg p\).
03

- Simplify the Expression

We now have \((eg q \wedge (eg p \vee q)) \), which needs to be simplified. Using distributive properties, this simplifies to: \((eg q \wedge eg p) \vee (eg q \wedge q)\). Notice that \((eg q \wedge q)\) is always false (a contradiction), so we can ignore it. Thus, the expression simplifies to: \((eg q \wedge eg p)\).
04

- Evaluate the Outer Implication

We are left with \((eg q \wedge eg p) \rightarrow eg p\). By the definition of implication, this is equivalent to \(eg (eg q \wedge eg p) \vee eg p\). Simplify inside the negation: \((q \vee p) \vee eg p\).
05

- Use Associative Properties

Apply the associative properties to simplify: \((q \vee p) \vee eg p = q \vee (p \vee eg p)\). Since \(p \vee eg p\) is always true (a tautology), the expression simplifies to \(q \vee \text{True} = \text{True}\). Hence, \(q \vee \text{True}\) is always true.
06

- Conclusion

Since the expression is always true for any values of \(p\) and \(q\), the given formula \(eg q \wedge (p \rightarrow q)) \rightarrow eg p \) is a tautology.

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Key Concepts

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

Logical Implications
In logic, an implication is an expression of the form \( A \rightarrow B \), which reads as 'If A, then B'. The implication is only false when A is true and B is false. Otherwise, it is true for all other cases. Implications can be rewritten to better analyze logical expressions. For instance, \( A \rightarrow B \) can be rewritten as \( eg A \vee B \), which reads as 'Not A or B'. This equivalence is helpful when simplifying logical expressions.
To fully understand how an implication works, consider a simple example:
- If it rains (A), then I will carry an umbrella (B).
If it rains and I do not carry an umbrella, the statement is false. If it does not rain, or it does rain and I do carry an umbrella, the statement is true.
Distributive Properties
The distributive property is an important rule in logic. It allows us to simplify complex logical expressions. The distributive properties in logic are:
- \( A \wedge (B \vee C) = (A \wedge B) \vee (A \wedge C) \)
- \( A \vee (B \wedge C) = (A \vee B) \wedge (A \vee C) \)
These properties help to transform combinations of logical connectors \'and\' (\( \wedge \)) and \'or\' (\( \vee \)).
For example, consider the expression \( eg q \wedge (eg p \vee q) \). Using the distributive property:
\( eg q \wedge (eg p \vee q) = (eg q \wedge eg p) \vee (eg q \wedge q) \).
This step greatly simplifies the expression, making subsequent evaluations easier. Using distributive properties can be very powerful when dealing with large and complex logical expressions.
Associative Properties
Associative properties in logic show how we group elements in logical expressions. They state that the grouping of variables does not change the outcome. For logical AND and OR, the associative properties are:
- \( (A \wedge B) \wedge C = A \wedge (B \wedge C) \)
- \( (A \vee B) \vee C = A \vee (B \vee C) \)
These properties allow us to rearrange expressions without changing their truth value.
For example, consider the expression \( (q \vee p) \vee eg p \). Using the associative property, we can change it to \( q \vee (p \vee eg p) \). This is especially useful because some sub-expressions may simplify to a known truth value. Here, \( p \vee eg p = \text{True} \), so the overall expression simplifies to \( q \vee \text{True} = \text{True} \). Thus, we can determine that the entire expression is true regardless of the values of p and q.
Truth Tables
A truth table is a tool used in logic to determine the truth value of a logical expression based on all possible truth values of its variables. It systematically lists the outcomes for every combination of truth values. To create a truth table:
- Identify all variables in the expression.
- Determine the number of possible combinations of truth values (2^n for n variables).
- List all possible combinations and compute the truth value for each component of the expression.
Using the problem's expression as an example, we have:

1. \((eg q \wedge (p \rightarrow q)) \rightarrow eg p\)

- Variables: p and q. There are 4 combinations: (T, T), (T, F), (F, T), (F, F).
- For each combination, compute \( p \rightarrow q \), \( eg q \), \( eg q \wedge (p \rightarrow q) \), and then \( (eg q \wedge (p \rightarrow q)) \rightarrow eg p \).
This step-by-step analysis provides a comprehensive understanding of whether the expression is a tautology. Truth tables help visualize logical statements and validate their outcomes.

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Most popular questions from this chapter

Exercises \(40-44\) deal with the translation between system specification and logical expressions involving quantifiers. Express each of these system specifications using predicates, quantifiers, and logical connectives. a) When there is less than 30 megabytes free on the hard disk, a warning message is sent to all users. b) No directories in the file system can be opened and no files can be closed when system errors have been detected. c) The file system cannot be backed up if there is a user currently logged on. d) Video on demand can be delivered when there are at least 8 megabytes of memory available and the connection speed is at least 56 kilobits per second.

Prove that between every rational number and every irrational number there is an irrational number.

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For each of these arguments determine whether the argument is correct or incorrect and explain why. a) All students in this class understand logic. Xavier is a student in this class. Therefore, Xavier understands logic. b) Every computer science major takes discrete math- ematics. Natasha is taking discrete mathematics. Therefore, Natasha is a computer science major. c) All parrots like fruit. My pet bird is not a parrot. Therefore, my pet bird does not like fruit. d) Everyone who eats granola every day is healthy. Linda is not healthy. Therefore, Linda does not eagranola every day.

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