Hausdorff implies US
This article gives the statement and possibly, proof, of an implication relation between two topological space properties. That is, it states that every topological space satisfying the first topological space property (i.e., Hausdorff space) must also satisfy the second topological space property (i.e., US-space)
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Given: A Hausdorff space . A convergent sequence with limit and limit .
To prove: .
Proof: Suppose . Then, by Hausdorffness of , there exist disjoint open subsets and such that .
The definition of limit tells us that for all but finitely many , , and for all but finitely many , . Hence, there exists a value of for which , which is a contradiction since and are disjoint. This completes the contradiction, and hence the proof.