Exercise 8. Subspaces product topology Let A be a subspace of X and let B be a subspace of Y. We equip A and B with the subspace topologies. Prove that the product topology on Ax B is the same as the topology Ax B inherits as a subspace of X x Y.

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topology exercice 8

**Exercises on Advanced Topology Concepts**

**Exercise 7: Basis and Comparable Topology**

Let \( X = \mathbb{R} \) and \( K = \left\{ \frac{1}{n}; n \in \mathbb{N} \right\} \). Consider the following collections on \( X \):

- \( \mathcal{B} = \{ [a, b); a, b \in \mathbb{R}, a < b \} \)
- \( \mathcal{B}' = \{ (a, b]; a, b \in \mathbb{R}, a < b \} \)
  
And

\[ \mathcal{B}'' = \{ [a, b); a, b \in \mathbb{R}, a < b \} \cup \{ [a, b) \backslash K; a, b \in \mathbb{R}, a < b \} \]

Knowing that \( \mathcal{B} \) and \( \mathcal{B}' \) are bases for some topology on \( X \), prove that \( \mathcal{B}'' \) is a basis for a topology on \( X \). Furthermore, let \( \tau, \tau', \) and \( \tau'' \) denote the topologies on \( X \) generated by \( \mathcal{B}, \mathcal{B}', \) and \( \mathcal{B}'' \), respectively. Prove that \( \tau' \) and \( \tau'' \) are finer than \( \tau \), and that \( \tau' \) and \( \tau'' \) are not comparable.

**Exercise 8: Subspaces Product Topology**

Let \( A \) be a subspace of \( X \) and let \( B \) be a subspace of \( Y \). We equip \( A \) and \( B \) with the subspace topologies. Prove that the product topology on \( A \times B \) is the same as the topology \( A \times B \) inherits as a subspace of \( X \times Y \).

**Exercise 9: Closed Product Topology**

Let \( X \) and \( Y \) be topological spaces, \( A, U \) be subsets of \( X \), and \( B \
Transcribed Image Text:**Exercises on Advanced Topology Concepts** **Exercise 7: Basis and Comparable Topology** Let \( X = \mathbb{R} \) and \( K = \left\{ \frac{1}{n}; n \in \mathbb{N} \right\} \). Consider the following collections on \( X \): - \( \mathcal{B} = \{ [a, b); a, b \in \mathbb{R}, a < b \} \) - \( \mathcal{B}' = \{ (a, b]; a, b \in \mathbb{R}, a < b \} \) And \[ \mathcal{B}'' = \{ [a, b); a, b \in \mathbb{R}, a < b \} \cup \{ [a, b) \backslash K; a, b \in \mathbb{R}, a < b \} \] Knowing that \( \mathcal{B} \) and \( \mathcal{B}' \) are bases for some topology on \( X \), prove that \( \mathcal{B}'' \) is a basis for a topology on \( X \). Furthermore, let \( \tau, \tau', \) and \( \tau'' \) denote the topologies on \( X \) generated by \( \mathcal{B}, \mathcal{B}', \) and \( \mathcal{B}'' \), respectively. Prove that \( \tau' \) and \( \tau'' \) are finer than \( \tau \), and that \( \tau' \) and \( \tau'' \) are not comparable. **Exercise 8: Subspaces Product Topology** Let \( A \) be a subspace of \( X \) and let \( B \) be a subspace of \( Y \). We equip \( A \) and \( B \) with the subspace topologies. Prove that the product topology on \( A \times B \) is the same as the topology \( A \times B \) inherits as a subspace of \( X \times Y \). **Exercise 9: Closed Product Topology** Let \( X \) and \( Y \) be topological spaces, \( A, U \) be subsets of \( X \), and \( B \
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