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- Jan 17, 2013

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I can't understand the two marked phrasesThe positive integers \(\displaystyle \mathbb{Z}^+\) form an ordered set with a smallest element .The order topology on \(\displaystyle \mathbb{Z}^+\) is the discrete topology , for every one-point set is open : if n>1 then the one-open set \(\displaystyle \{n\}= (n-1,n+1) \) is a basis element ; and if n=1 , the one-point set \(\displaystyle \{1\}=[1,2)\) is a basis element .