Lecture 2 - Conditionals and Biconditionals

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What is a statement of the form P ⇒ Q called?

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An implication or a conditional.

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Implications and Conditionals

What is a statement of the form P ⇒ Q called?

An implication or a conditional.

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Order of Connectives

How would you insert implied parentheses in the expression P ∨ ∼ Q ⇔ R ⇒ S?

(P ∨ ∼ Q) ⇔ (R ⇒ S)

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Propositional Form

In the example, what does P represent?

P represents 'My son cleans his room.'

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Biconditionals

How do we read the biconditional P ⇔ Q?

We read P ⇔ Q as 'P if and only if Q'.

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Ways of Expressing P ⇒ Q

What is one way to express the implication P ⇒ Q?

If P, then Q.

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Propositional Form

What is the propositional form of the statement: 'If b is an integer, then b is either even or odd'?

Let P be 'b is an integer' and Q be 'b is either even or odd'. The propositional form is P ⇒ Q.

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Understanding Conditionals

Provide an example of a conditional that is false due to the antecedent.

If π is equal to 3, then Paris is the capital of France.

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Biconditionals

How can 'P is necessary and sufficient condition for Q' be expressed symbolically?

It can be expressed as P ⇔ Q.

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Biconditionals

What is the truth condition for the biconditional P ⇔ Q?

The biconditional P ⇔ Q is true if P and Q have the same truth value, and false otherwise.

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Ways of Expressing P ⇔ Q

What does 'P if and only if Q' express?

It expresses that P is true exactly when Q is true.

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Understanding Conditionals

How can the statement 'A necessary condition for a group G to be cyclic is that G is abelian' be expressed in the form P ⇒ Q?

Let P be 'G is abelian' and Q be 'G is cyclic'. Therefore, the statement can be written as P ⇒ Q.

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Implications and Conditionals

What is a statement of the form P ⇒ Q called?

An implication or a conditional.

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Understanding Conditionals

What does the statement P ⇒ Q imply when P is false?

When P is false, Q can be either true or false; the implication P ⇒ Q is still considered true.

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Ways of Expressing P ⇔ Q

How can 'P if and only if Q' be alternatively expressed?

It can be expressed as 'P is equivalent to Q'.

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Propositional Form

What is the propositional form of the statement: 'If p is a prime number that divides ab, then p divides a or b'?

Let R be 'p is a prime number that divides ab' and S be 'p divides a or b'. The propositional form is R ⇒ S.

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Truth Values of Implications

When is the implication P ⇒ Q false?

When P is true and Q is false.

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Biconditionals

What does 'P if and only if Q' signify?

'P if and only if Q' signifies that P is true exactly when Q is true, establishing a biconditional relationship.

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Biconditionals

What is a necessary and sufficient condition for a graph G to be a tree?

A necessary and sufficient condition for the graph G to be a tree is that G is connected and every edge of G is a bridge.

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Order of Connectives

How would you insert implied parentheses in the expression P ⇒∼ Q ∨ R ⇔ S?

(P ⇒ (∼ Q ∨ R)) ⇔ S

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Understanding Conditionals

How can the implication P ⇒ Q be interpreted?

It can be interpreted as 'Whenever P is true, Q must also be true, but if P is false, anything can happen.'

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Ways of Expressing P ⇒ Q

What does P implies Q mean?

P implies Q.

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Truth Values of Implications

What happens to the truth value of a conditional when the conclusion is true?

The truth value of the premise does not matter; the conditional will be true.

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Biconditionals

What is the truth value of 'The number 2 is equal to 8 if and only if 49 is a perfect square'?

False, because 2 is not equal to 8 and 49 is a perfect square.

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Understanding Conditionals

What does P represent in the example given?

The integer 3 is odd.

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Ways of Expressing P ⇒ Q

What does P only if Q signify?

P only if Q.

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Ways of Expressing P ⇒ Q

Provide an example of a conditional statement.

If Isaac Newton was born in 1642, then 3 · 5 = 15.

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Understanding Conditionals

How can the statement 'A set S is infinite if S has an uncountable subset' be expressed in the form P ⇒ Q?

Let P be 'S has an uncountable subset' and Q be 'S is infinite'. Therefore, the statement can be written as P ⇒ Q.

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Biconditionals

What is the truth value of 'The number π is equal to 22/7 if and only if √2 is a rational number'?

False, because π is not equal to 22/7 and √2 is not a rational number.

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Understanding Conditionals

What does Q represent in the example given?

The integer 57 is prime.

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Understanding Conditionals

What is a conditional statement?

A conditional statement is an expression of the form 'If P, then Q', where P is the antecedent and Q is the consequent.

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Truth Values of Implications

What happens to the truth value of a conditional when the premise is false?

The truth value of the conclusion does not matter; the conditional will be true.

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Implications and Conditionals

Can a conditional be true without a connection between the antecedent and the consequent?

Yes, a conditional may be true even when there is no connection between the antecedent and the consequent.

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Truth Values of Implications

When is the implication P ⇒ Q false?

When P is true and Q is false.

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Ways of Expressing P ⇒ Q

How can you express Q in relation to P?

Q if P.

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Ways of Expressing P ⇒ Q

How can you express the implication P ⇒ Q?

The implication P ⇒ Q can be expressed as 'If P, then Q' or 'Q is true whenever P is true'.

p.4
Understanding Conditionals

Give an example of a conditional where the antecedent and consequent are unrelated.

If sin π is equal to 1, then 6 is prime.

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Order of Connectives

What is the order of connectives applied in logical expressions?

The connectives ∼, ∧, ∨, ⇒, ⇔ are always applied in that order.

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Understanding Conditionals

How can the statement 'S is compact is sufficient for S to be bounded' be expressed in the form P ⇒ Q?

Let P be 'S is compact' and Q be 'S is bounded'. Therefore, the statement can be written as P ⇒ Q.

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Converse of Implications

What is the converse of the statement 'If 5 is an even integer, then 7 is an odd integer'?

The converse is 'If 7 is an odd integer, then 5 is an even integer.'

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Biconditionals

What does a biconditional statement express?

A biconditional statement expresses that both conditions are equivalent, typically written as 'P if and only if Q'.

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Understanding Conditionals

What is an example of a true conditional with a true antecedent?

If 13 is greater than 7, then 2 + 3 = 5.

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Converse of Implications

What is the converse of the implication P ⇒ Q?

The converse is the implication Q ⇒ P.

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Ways of Expressing P ⇔ Q

What is meant by 'P is necessary and sufficient condition for Q'?

It means that P must be true for Q to be true and vice versa.

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Ways of Expressing P ⇔ Q

What is another way to say 'P if, but only if Q'?

It can also be stated as 'P is equivalent to Q'.

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Converse of Implications

What is the converse of an implication?

The converse of an implication P ⇒ Q is Q ⇒ P.

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Biconditionals

What is the truth value of 'The number 5 is an odd integer if and only if 7 is an odd integer'?

True, because both 5 and 7 are odd integers.

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Ways of Expressing P ⇒ Q

What does it mean when we say P is sufficient for Q?

P is sufficient for Q.

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Ways of Expressing P ⇒ Q

What does Q is necessary for P indicate?

Q is necessary for P.

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Propositional Form

In the example, what does Q represent?

Q represents 'I will give him ice cream.'

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Truth Values of Implications

What are truth values in the context of implications?

Truth values determine the validity of an implication based on the truth of P and Q; the implication is false only when P is true and Q is false.

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Truth Values of Implications

What determines the truth value of P ⇒ Q in a conditional?

The truth value of P ⇒ Q depends only on the truth value of components P and Q, not on their interpretation.

Study Smarter, Not Harder
Study Smarter, Not Harder