Feller Peter, Lewark Lukas, Lobb Andrew
ETH Zurich, Rämistrasse 101, 8092 Zurich, Switzerland.
Mathematical Institute, University of Bern, Alpeneggstr. 22, 3012 Bern, Switzerland.
Math Ann. 2023;385(1-2):481-510. doi: 10.1007/s00208-021-02328-x. Epub 2022 Jan 11.
We prove that any link admitting a diagram with a single negative crossing is strongly quasipositive. This answers a question of Stoimenow's in the (strong) positive. As a second main result, we give a simple and complete characterization of link diagrams with quasipositive canonical surface (the surface produced by Seifert's algorithm). As applications, we determine which prime knots up to 13 crossings are strongly quasipositive, and we confirm the following conjecture for knots that have a canonical surface realizing their genus: a knot is strongly quasipositive if and only if the Bennequin inequality is an equality.
我们证明,任何允许具有单个负交叉点的图的链环都是强拟正的。这在(强)正方向上回答了斯托伊梅诺夫的一个问题。作为第二个主要结果,我们给出了具有拟正典范曲面(由赛弗特算法产生的曲面)的链环图的简单而完整的特征描述。作为应用,我们确定了13交叉以内的哪些素纽结是强拟正的,并且我们对于具有实现其亏格的典范曲面的纽结证实了以下猜想:一个纽结是强拟正的当且仅当本内昆不等式取等号。