most recent 30 from http://mathoverflow.net 2013-05-21T12:13:46Z http://mathoverflow.net/feeds/question/98640 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/98640/why-is-tb-0-for-boundary-of-a-convex-surface kln 2012-06-02T08:08:18Z 2012-06-02T10:13:52Z

<p>Why is $tb(K)$ (Thurston-Bennequin invariant) of a Legendrian knot $K$ which is the boundary of a convex surface $\Sigma$ is negative in a contact 3 manifold?</p>

http://mathoverflow.net/questions/98640/why-is-tb-0-for-boundary-of-a-convex-surface/98648#98648 Marco Golla 2012-06-02T10:13:52Z 2012-06-02T10:13:52Z

<p>If the boundary of a convex surface is Legendrian, then we can see the Thurston-Bennequin number directly from the dividing curves $\Gamma$, in the sense that: <code>$tb(L) = \#(\Gamma \cap L)/2$</code>.</p> <p>This is proved, for example, in Etnyre's <a href="http://people.math.gatech.edu/~etnyre/preprints/papers/surfaces.pdf" rel="nofollow">notes</a>, Theorem 2.30.</p>