most recent 30 from http://mathoverflow.net 2013-06-19T04:43:45Z http://mathoverflow.net/feeds/question/49853 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/49853/finite-index-in-f-m-implies-non-trivial-intersection Bazooka 2010-12-19T06:22:35Z 2010-12-19T06:22:35Z

<p>I was looking at a <a href="http://www.unige.ch/math/folks/arjantse/Abs/revst-int.psBlockquote" rel="nofollow">paper</a>, and I saw this claim, </p> <blockquote> <p>It is obvious that if $H$ has finite index in $F_m$ then $H$ has non-trivial intersection with each of the non-trivial subgroups of $F_m$. </p> </blockquote> <p>Why is this immediate?</p>