M. Ishikawa

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math.GT2026

Topology of the links of cDV singularities of types $c A_{n}$ for $n > 0$ and $c D_{n}$ for $n > 4$

Masaharu Ishikawa, Atsuko Katanaga

We show that the second integral homology group of the link of an isolated compound Du Val (cDV, for short) singularity of type $c A_{n}$ is either trivial or a torsion-free abelian g…

math.GT2024

Twist spun knots of twist spun knots of classical knots

Mizuki Fukuda, Masaharu Ishikawa

A $k$ -twist spun knot is an $n + 1$ -dimensional knot in the $n + 3$ -dimensional sphere which is obtained from an $n$ -dimensional knot in the $n + 2$ -dimensional sphere by applying an ope…

math.GT2024

Distinguishing 2-knots admitting circle actions by fundamental groups

Mizuki Fukuda, Masaharu Ishikawa

A 2-sphere embedded in the 4-sphere invariant under a circle action is called a branched twist spin. A branched twist spin is constructed from a 1-knot in the 3-sphere and a pair o…

math.GT2024

Combinatorial cusp count and clover invariants

Sebastian Baader, Masaharu Ishikawa

We construct efficient topological cobordisms between torus links and large connected sums of trefoil knots. As an application, we show that the signature invariant $I ¨ _{I ¨} $ at $Ï=…

Topology of the links of cDV singularities of types cAn​ for n>0 and cDn​ for n>4

Twist spun knots of twist spun knots of classical knots

Distinguishing 2-knots admitting circle actions by fundamental groups

Combinatorial cusp count and clover invariants

Topology of the links of cDV singularities of types $c A_{n}$ for $n > 0$ and $c D_{n}$ for $n > 4$