## Incompressibility criteria for spun-normal surfaces

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- by Nathan M. Dunfield and Stavros Garoufalidis PDF
- Trans. Amer. Math. Soc.
**364**(2012), 6109-6137 Request permission

## Abstract:

We give a simple sufficient condition for a spun-normal surface in an ideal triangulation to be incompressible, namely that it is a vertex surface with nonempty boundary which has a quadrilateral in each tetrahedron. While this condition is far from being necessary, it is powerful enough to give two new results: the existence of alternating knots with noninteger boundary slopes, and a proof of the Slope Conjecture for a large class of 2-fusion knots.

While the condition and conclusion are purely topological, the proof uses the Culler-Shalen theory of essential surfaces arising from ideal points of the character variety, as reinterpreted by Thurston and Yoshida. The criterion itself comes from the work of Kabaya, which we place into the language of normal surface theory. This allows the criterion to be easily applied, and gives the framework for proving that the surface is incompressible.

We also explore which spun-normal surfaces arise from ideal points of the deformation variety. In particular, we give an example where no vertex or fundamental surface arises in this way.

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## Additional Information

**Nathan M. Dunfield**- Affiliation: Department of Mathematics, MC-382, University of Illinois, 1409 W. Green Street, Urbana, Illinois 61801
- MR Author ID: 341957
- ORCID: 0000-0002-9152-6598
- Email: nathan@dunfield.info
**Stavros Garoufalidis**- Affiliation: School of Mathematics, Georgia Institute of Technology, Atlanta, Georgia 30332-0160
- Email: stavros@math.gatech.edu
- Received by editor(s): February 23, 2011
- Received by editor(s) in revised form: March 2, 2011, and June 10, 2011
- Published electronically: May 18, 2012
- © Copyright 2012
American Mathematical Society

The copyright for this article reverts to public domain 28 years after publication. - Journal: Trans. Amer. Math. Soc.
**364**(2012), 6109-6137 - MSC (2010): Primary 57N10; Secondary 57M25, 57M27
- DOI: https://doi.org/10.1090/S0002-9947-2012-05663-7
- MathSciNet review: 2946944