Difference between revisions of "Heine-Borel Theorem"

Latest revision as of 11:30, 9 April 2019

The Heine-Borel theorem is an important theorem in elementary topology.

Let $E$ be any subset of $\mathbb R^n$ . Then $E$ is compact if and only if $E$ is closed and bounded.

This statement does not hold if $\mathbb R^n$ is replaced by an arbitrary metric space $X$ . However, a modified version of the theorem does hold:

Let $X$ be any metric space, and let $E$ be a subset of $X$ . Then $E$ is compact if and only if $E$ is closed and totally bounded.

In $\mathbb R^n$ the totally bounded sets are precisely the bounded sets, so this new formulation does indeed imply the original theorem.

@@ Line 1: / Line 1: @@
-The '''Heine-Borel theorem''' is an important theorem in elementary [[Topology]].
+The '''Heine-Borel theorem''' is an important theorem in elementary [[topology]].
 ==Statement==
-Let <math>X</math> be a [[Metric|metric space]]
+Let <math>E</math> be any [[subset]] of <math>\mathbb R^n</math>.  Then <math>E</math> is [[compact set | compact]] if and only if <math>E</math> is [[closed]] and [[bounded]].
-Let <math>E\subset X</math>
+This statement does ''not'' hold if <math>\mathbb R^n</math> is replaced by an arbitrary metric space <math>X</math>. However, a modified version of the theorem does hold:
-Then
+Let <math>X</math> be any metric space, and let <math>E</math> be a subset of <math>X</math>. Then <math>E</math> is compact if and only if <math>E</math> is closed and [[totally bounded]].
-(1) <math>E</math> is closed and bounded if and only if
+In <math>\mathbb R^n</math> the totally bounded sets are precisely the bounded sets, so this new formulation does indeed imply the original theorem.
-(2) <math>E</math> is [[Compact set|compact]]
+==See Also==
 {{stub}}
 [[Category:Topology]]
+[[Category: Theorems]]