Theorem 8.9. Let f : X Y be a continuous, surjective function. If X is connected, then Y is connected.

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter5: Rings, Integral Domains, And Fields
Section5.4: Ordered Integral Domains
Problem 1E: Complete the proof of Theorem 5.30 by providing the following statements, where and are arbitrary...
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Theorem 8.9. Let f : X → Y be a continuous, surjective function. If X is connected,
then Y is connected.
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 An B = An B = Ø. Thus B does not contain any limit points of A, and A does not
contain any limit points
are separated sets.
B. The notation
A | B means X = AU B and A and
Theorem 8.1. The following are equivalent:
(1) X is connected.
(2) There is no continuous function f : X → Rstd 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«}aea of X there exist a finite
number of the Ua's, {U«,, U«,, Uaz,.., Ua, } such that p E Ug,, q E U,, and for each
i < n, Ua, n Uai41 + Ø.
di+1
Theorem 8.3. The space Rstd is connected.
Theorem 8.5. Let{C«}aea be a collection of connected subsets ofX, and let E be another
connected subset of X such that for each a in à, En Ca # Ø. Then E U (Urea Ca) is
соппеcted.
αελ
Theorem 8.6. Let C be a connected subset of the topological space X. If D is a subset of
X such that C CDC C, then D is connected.
Transcribed Image Text:Theorem 8.9. Let f : X → Y be a continuous, surjective function. If X is connected, then Y is connected. 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 An B = An B = Ø. Thus B does not contain any limit points of A, and A does not contain any limit points are separated sets. B. The notation A | B means X = AU B and A and Theorem 8.1. The following are equivalent: (1) X is connected. (2) There is no continuous function f : X → Rstd 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«}aea of X there exist a finite number of the Ua's, {U«,, U«,, Uaz,.., Ua, } such that p E Ug,, q E U,, and for each i < n, Ua, n Uai41 + Ø. di+1 Theorem 8.3. The space Rstd is connected. Theorem 8.5. Let{C«}aea be a collection of connected subsets ofX, and let E be another connected subset of X such that for each a in à, En Ca # Ø. Then E U (Urea Ca) is соппеcted. αελ Theorem 8.6. Let C be a connected subset of the topological space X. If D is a subset of X such that C CDC C, then D is connected.
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