Arrow diagrams on spherical curves and computations

We give a definition of an integer-valued function [Formula: see text] derived from arrow diagrams for the ambient isotopy classes of oriented spherical curves. Then, we introduce certain elements of the free [Formula: see text]-module generated by the arrow diagrams with at most [Formula: see text] arrows, called relators of Type ([Formula: see text]) (([Formula: see text]), ([Formula: see text]), ([Formula: see text]) or ([Formula: see text]), respectively), and introduce another function [Formula: see text] to obtain [Formula: see text]. One of the main results shows that if [Formula: see text] vanishes on finitely many relators of Type ([Formula: see text]) (([Formula: see text]), ([Formula: see text]), ([Formula: see text]) or ([Formula: see text]), respectively), then [Formula: see text] is invariant under the deformation of type RI (strong RI[Formula: see text]I, weak RI[Formula: see text]I, strong RI[Formula: see text]I[Formula: see text]I or weak RI[Formula: see text]I[Formula: see text]I, respectively). The other main result is that we obtain new functions of arrow diagrams with up to six arrows explicitly. This computation is done with the aid of computers.

On framings of links in 3-manifolds

We show that the only way of changing the framing of a link by ambient isotopy in an oriented $3$ -manifold is when the manifold has a properly embedded non-separating $S^{2}$ . This change of framing is given by the Dirac trick, also known as the light bulb trick. The main tool we use is based on McCullough’s work on the mapping class groups of $3$ -manifolds. We also relate our results to the theory of skein modules.

6. Unknot or knot to be?

‘Unknot or knot to be?’ explains that a knot is a smooth, simple, closed curve in 3D space. Being simple and closed means the curve does not cross itself except that its end returns to its start. All knots are topologically the same as a circle; what makes a circle knotted—or not—is how that circle has been placed into 3D space. The central problem of knot theory is a classification theorem: when is there an ambient isotopy between two knots or how do we show that no such isotopy exists? Key elements of knot theory are discussed, including the three Reidemeister moves, prime knots, adding knots, and the Alexander and Jones polynomials.

Space of chord diagrams on spherical curves

In this paper, we give a definition of [Formula: see text]-valued functions from the ambient isotopy classes of spherical/plane curves derived from chord diagrams, denoted by [Formula: see text]. Then, we introduce certain elements of the free [Formula: see text]-module generated by the chord diagrams with at most [Formula: see text] chords, called relators of Type (I) ((SI[Formula: see text]I), (WI[Formula: see text]I), (SI[Formula: see text]I[Formula: see text]I), or (WI[Formula: see text]I[Formula: see text]I), respectively), and introduce another function [Formula: see text] derived from [Formula: see text]. The main result (Theorem 1) shows that if [Formula: see text] vanishes for the relators of Type (I) ((SI[Formula: see text]I), (WI[Formula: see text]I), (SI[Formula: see text]I[Formula: see text]I), or (WI[Formula: see text]I[Formula: see text]I), respectively), then [Formula: see text] is invariant under the Reidemeister move of type RI (strong RI[Formula: see text]I, weak RI[Formula: see text]I, strong RI[Formula: see text]I[Formula: see text]I, or weak RI[Formula: see text]I[Formula: see text]I, respectively) that is defined in [N. Ito and Y. Takimura, [Formula: see text] and weak [Formula: see text] homotopies on knot projections, J. Knot Theory Ramifications 22 (2013) 1350085 14 pp].

Smoothing closed gridded surfaces embedded in ℝ4

We say that a topological [Formula: see text]-manifold [Formula: see text] is a cubical [Formula: see text]-manifold if it is contained in the [Formula: see text]-skeleton of the canonical cubulation [Formula: see text] of [Formula: see text] ([Formula: see text]). In this paper, we prove that any closed, oriented cubical [Formula: see text]-manifold has a transverse field of 2-planes in the sense of Whitehead and therefore it is smoothable by a small ambient isotopy.

Presentation of immersed surface-links by marked graph diagrams

It is well known that surface-links in [Formula: see text]-space can be presented by diagrams on the plane of [Formula: see text]-valent spatial graphs with makers on the vertices, called marked graph diagrams. In this paper, we extend the method of presenting surface-links by marked graph diagrams to presenting immersed surface-links. We also give some moves on marked graph diagrams that preserve the ambient isotopy classes of their presenting immersed surface-links.

Sticky Cantor sets in ℝd

A subset of [Formula: see text] is called “sticky” if it cannot be isotoped off of itself by a small ambient isotopy. Sticky wild Cantor sets are constructed in [Formula: see text] for each [Formula: see text].

Classification of book representations of K6

A book representation of a graph is a particular way of embedding a graph in three-dimensional space so that the vertices lie on a circle and the edges are chords on disjoint topological disks. We describe a set of operations on book representations that preserves ambient isotopy, and apply these operations to [Formula: see text], the complete graph with six vertices. We prove there are exactly 59 distinct book representations for [Formula: see text], and we identify the number and type of knotted and linked cycles in each representation. We show that book representations of [Formula: see text] contain between one and seven links, and up to nine knotted cycles. Furthermore, all links and cycles in a book representation of [Formula: see text] have crossing number at most four.

Rectangular Seifert circles and arcs system

Rectangular diagrams of links are link diagrams in the plane ℝ2 such that they are composed of vertical line segments and horizontal line segments and vertical segments go over horizontal segments at all crossings. Cromwell and Dynnikov showed that rectangular diagrams of links are useful for deciding whether a given link is split or not, and whether a given knot is trivial or not. We show in this paper that an oriented link diagram D with c(D) crossings and s(D) Seifert circles can be deformed by an ambient isotopy of ℝ2 into a rectangular diagram with at most c(D) + 2s(D) vertical segments, and that, if D is connected, at most 2c(D) + 2 - w(D) vertical segments, where w(D) is a certain non-negative integer. In order to obtain these results, we show that the system of Seifert circles and arcs substituting for crossings can be deformed by an ambient isotopy of ℝ2 so that Seifert circles are rectangles composed of two vertical line segments and two horizontal line segments and arcs are vertical line segments, and that we can obtain a single circle from a connected link diagram by smoothing operations at the crossings regardless of orientation.