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The C-complex clasp number of links. (English) Zbl 1447.57002

Summary: In the 1980s, Daryl Cooper introduced the notion of a C-complex (or clasp-complex) bounded by a link and explained how to compute signatures and polynomial invariants using a C-complex. Since then, this has been extended by works of Cimasoni, Florens, Mellor, Melvin, Conway, Toffoli, Friedl, and others to compute other link invariants. Informally, a C-complex is a union of surfaces which are allowed to intersect each other in clasps. We study the minimal number of clasps amongst all C-complexes bounded by a fixed link \(L\). This measure of complexity is related to the number of crossing changes needed to reduce \(L\) to a boundary link. We prove that if \(L\) is a 2-component link with nonzero linking number, then the linking number determines the minimal number of clasps amongst all C-complexes. In the case of 3-component links, the triple linking number provides an additional lower bound on the number of clasps in a C-complex.

MSC:

57K10 Knot theory

References:

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[2] D. Cimasoni and V. Florens, “Generalized Seifert surfaces and signatures of colored links”, Trans. Amer. Math. Soc. 360:3 (2008), 1223-1264. · Zbl 1132.57004 · doi:10.1090/S0002-9947-07-04176-1
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[7] B. Mellor and P. Melvin, “A geometric interpretation of Milnor”s triple linking numbers”, Algebr. Geom. Topol. 3 (2003), 557-568. · Zbl 1040.57007 · doi:10.2140/agt.2003.3.557
[8] J. Milnor, “Isotopy of links”, pp. 280-306 in Algebraic geometry and topology: a symposium in honor of S. Lefschetz, Princeton Univ. Press, 1957. · Zbl 0080.16901
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[10] T. · Zbl 0291.55002
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