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Section 2.2 Exercises

Checkpoint 2.2.1.

Let \(P(x,y)\) denote \(x \geq y\text{.}\) Determine whether the following statement are true or false; justify your answer.
  1. \(\forall x, y \in \mathbb{N}, P(x,y)\)
  2. \(\forall x \in \mathbb{N}, \exists y \in \mathbb{N}\) such that \(P(x,y)\)
  3. \(\exists x \in \mathbb{N}\) such that \(\forall y \in \mathbb{N}\text{,}\) \(P(x,y)\)
  4. \(\exists x,y \in \mathbb{N}\) such that \(P(x,y)\)

Checkpoint 2.2.2.

Write down the negation of the following statements, moving the negation symbol \(\lnot\) as far to the right as possible. Use symbolic logic notation.
  1. \(\displaystyle \forall x \in A \left [ p(x) \implies q(x) \right ]\)
  2. \(\exists x \in A \) such that \(\left [ \left ( \lnot p(x)\right ) \land q(x) \right ]\)
  3. \(\displaystyle \forall x \in A \left [ p(x) \implies \left ( \exists y \in B \text{ such that } \left [ q(x,y) \land r(x,y) \right] \right ) \right ]\)

Checkpoint 2.2.3.

Rewrite the following sentence using symbolic logic notation for the logical connectives and quantifiers (\(\mathcal{F}\) denotes the set of all functions \(\mathbb{R} \to \mathbb{R}\)).
“For any function \(f \in \mathcal{F}\) that is continuous on \([a, b]\text{,}\) there is some \(c \in [a,b]\) such that for all \(x\in [a,b]\text{,}\) \(f(c) \leq f(x)\text{.}\)