(3) X is not the union of two disjoint non-empty separated sets. (4) X is not the union of two disjoint non-empty closed sets. (5) The only subsets of X that are both closed and open in X are the empty set and X itself. (6) For every pair of points p and q and every open cover {Uq}aea of X there exist a finite number of the Uq's, {U«,, Uaz, Uaz»….. , Uan} such that p E Ua,, q E Ugn; and for each i < n, Ua; n Uai+1 + Ø.

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How do I show (4),(5),(6) in 8.1?

**Definition.** Let \( X \) be a topological space. Then \( X \) is **connected** if and only if \( X \) is not the union of two disjoint non-empty open sets.

**Definition.** Let \( X \) be a topological space. Subsets \( A, B \) in \( X \) are **separated** if and only if \( \overline{A} \cap B = A \cap \overline{B} = \varnothing \). Thus \( B \) does not contain any limit points of \( A \), and \( A \) does not contain any limit points of \( B \). The notation \( X = A \mid B \) means \( X = A \cup B \) and \( A \) and \( B \) are separated sets.

**Theorem 8.1.** The following are equivalent:

1. \( X \) is connected.

2. There is no continuous function \( f : X \to \mathbb{R}_{std} \) such that \( f(X) = \{0, 1\} \).

3. \( X \) is not the union of two disjoint non-empty separated sets.

4. \( X \) is not the union of two disjoint non-empty closed sets.

5. The only subsets of \( X \) that are both closed and open in \( X \) are the empty set and \( X \) itself.

6. For every pair of points \( p \) and \( q \) and every open cover \(\{U_\alpha\}_{\alpha \in \Lambda} \) of \( X \) there exist a finite number of the \( U_\alpha \)'s, \(\{U_{\alpha_1}, U_{\alpha_2}, U_{\alpha_3}, \ldots, U_{\alpha_n}\}\) such that \( p \in U_{\alpha_1}, q \in U_{\alpha_n} \), and for each \( i < n, U_{\alpha_i} \cap U_{\alpha_{i+1}} \neq \varnothing \).
Transcribed Image Text:**Definition.** Let \( X \) be a topological space. Then \( X \) is **connected** if and only if \( X \) is not the union of two disjoint non-empty open sets. **Definition.** Let \( X \) be a topological space. Subsets \( A, B \) in \( X \) are **separated** if and only if \( \overline{A} \cap B = A \cap \overline{B} = \varnothing \). Thus \( B \) does not contain any limit points of \( A \), and \( A \) does not contain any limit points of \( B \). The notation \( X = A \mid B \) means \( X = A \cup B \) and \( A \) and \( B \) are separated sets. **Theorem 8.1.** The following are equivalent: 1. \( X \) is connected. 2. There is no continuous function \( f : X \to \mathbb{R}_{std} \) such that \( f(X) = \{0, 1\} \). 3. \( X \) is not the union of two disjoint non-empty separated sets. 4. \( X \) is not the union of two disjoint non-empty closed sets. 5. The only subsets of \( X \) that are both closed and open in \( X \) are the empty set and \( X \) itself. 6. For every pair of points \( p \) and \( q \) and every open cover \(\{U_\alpha\}_{\alpha \in \Lambda} \) of \( X \) there exist a finite number of the \( U_\alpha \)'s, \(\{U_{\alpha_1}, U_{\alpha_2}, U_{\alpha_3}, \ldots, U_{\alpha_n}\}\) such that \( p \in U_{\alpha_1}, q \in U_{\alpha_n} \), and for each \( i < n, U_{\alpha_i} \cap U_{\alpha_{i+1}} \neq \varnothing \).
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