most recent 30 from http://mathoverflow.net 2013-05-20T09:30:32Z http://mathoverflow.net/feeds/question/108001 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/108001/a-basic-question-on-stone-cech-compactification-of-mathbbz Safoura 2012-09-24T19:22:33Z 2012-09-25T02:42:54Z

<p>Can the identity isomorphism on the additive group $\mathbb{Z}$ be extended to a non-identity semigroup isomorphism on $\beta\mathbb{Z}$, and still preserves $\beta\mathbb{Z}\setminus\mathbb{Z}$? Obviously this extension is discontinuous. </p>