Combining Lefschetz numbers with Euler classes - MathOverflow most recent 30 from http://mathoverflow.net2013-05-25T14:48:11Zhttp://mathoverflow.net/feeds/question/73379http://www.creativecommons.org/licenses/by-nc/2.5/rdfhttp://mathoverflow.net/questions/73379/combining-lefschetz-numbers-with-euler-classesCombining Lefschetz numbers with Euler classesAllen Knutson2011-08-22T06:19:37Z2011-08-22T06:19:37Z
<p>Given an $n$-manifold $M$ (say), we can talk about its Euler characteristic
$\chi(M)$.</p>
<ol>
<li><p>This can be generalized to the Euler number of any $n$-dimensional
bundle ${\mathcal V}$. Or indeed, the Euler class of any
$k$-dimensional oriented bundle.</p></li>
<li><p>Or, given a map $f:M\to M$, we can talk about its Lefschetz number,
where $\chi(M)$ is the Lefschetz number of the identity. </p></li>
<li><p>Or, we can compute $M$'s Betti numbers, and see $\chi(M)$ as the
alternating sum.</p></li>
</ol>
<p>I know how to combine 2 & 3, replacing the Betti number by $Tr(f|_{H^i(M)})$.</p>
<blockquote>
<p>Are 1 & 2 or 1 & 3 combinable? Or 1, 2, and 3?</p>
</blockquote>
<p>I don't have an application in mind, just the usual mathematician's hankering to take LCMs wherever possible.</p>