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For a signed cyclic graph [Formula: see text], we can construct a unique virtual link [Formula: see text] by taking the medial construction and converting 4-valent vertices of the medial graph to crossings according to the signs. If a virtual link can occur in this way then we say that the virtual link is graphical. In this paper, we shall prove that a virtual link [Formula: see text] is graphical if and only if it is checkerboard colorable. On the other hand, we introduce a polynomial [Formula: see text] for signed cyclic graphs, which is defined via a deletion-marking recursion. We shall establish the relationship between [Formula: see text] of a signed cyclic graph [Formula: see text] and the bracket polynomial of one of the virtual link diagrams associated with [Formula: see text]. Finally, we give a spanning subgraph expansion for [Formula: see text].

It is well known that Jones polynomial (hence, Kauffman bracket polynomial) of links is, in general, hard to compute. By now, Jones polynomials or Kauffman bracket polynomials of many link families have been computed, see [4, 7–11]. In recent years, the computer algebra (Maple) techniques were used to calculate link polynomials for various link families, see [7, 12–14]. In this paper, we try to design a maple program to calculate the explicit expression of the Kauffman bracket polynomial of Montesinos links. We first introduce a family of "ring of tangles" links, which includes Montesinos links as a special subfamily. Then, we provide a closed-form formula of Kauffman bracket polynomial for a "ring of tangles" link in terms of Kauffman bracket polynomials of the numerators and denominators of the tangles building the link. Finally, using this formula and known results on rational links, the Maple program is designed.

It is well known that Kauffman constructed a state model of the Jones polynomial based on unoriented link diagrams. In his approach, in order to obtain Jones polynomial one needs to calculate both the writhe and the Kauffman bracket. Stimulated by a paper of Altintas (An oriented state model for the Jones polynomial and its applications to alternating links, Appl. Math. Comput.194 (2007) 168–178), in this paper we present a state sum model based on oriented link diagrams. In our approach, we succeed in adding the writhe to the state sum model and need not to compute the writher any more. We further show that, via our state sum model, Jones polynomial of any link (alternating or not) is a special parametrization of the dichromatic polynomial of a weighted graph with two different edge weights.

It is well known that there is a one-to-one correspondence between signed plane graphs and link diagrams via the medial construction. The component number of the corresponding link diagram is however independent of the signs of the plane graph. Determining this number may be one of the first problems in studying links by using graphs. Some works in this aspect have been done. In this paper, we investigate the component number of links corresponding to lattices. Firstly we provide some general results on component number of links. Then, via these results, we proceed to determine the component number of links corresponding to lattices with free or periodic boundary conditions and periodic lattices with one cap (i.e. spiderweb graphs) or two caps.

Based on the connection with Alexander polynomial of special alternating links, Murasugi and Stoimenow introduced the Alexander polynomial of even graphs. In this paper, we study the Alexander polynomial of spatial even graphs with reflective symmetry. Roughly speaking, we prove that the Alexander polynomial of one half of a spatial even graph with reflective symmetry is a divisor of that of the whole spatial even graph. Then, we apply the result to a family of special alternating links, expressing the Alexander polynomial of such a link as the product of Alexander polynomials of two smaller special alternating links derived from the two isotopic "halves" of the original link.

Ichihara and Matsudo introduced the notions of [Formula: see text]-colorable links and the minimal coloring number for [Formula: see text]-colorable links, which is one of invariants for links. They proved that the lower bound of minimal coloring number of a non-splittable [Formula: see text]-colorable link is 4. In this paper, we show the minimal coloring number of any non-splittable [Formula: see text]-colorable link is exactly 4.

In this paper, we show that any 11-colorable knot has a diagram with a non-trivial 11-coloring such that at most six colors among eleven colors are assigned to arcs of the diagram.

In this paper, an expression for the Homfly polynomial of a classical pretzel link with a fixed orientation was obtained. As an application, we proved that a (p, q, r)-pretzel knot is achiral if and only if {p, q, r} = {2, 1, 1}, {-2, -1, -1}, {2, -1, 3}, {-2, 1, -3}, {1, -1, k}, {1, k, -2 -k} or {-1, -k, 2 + k}, where k is an odd integer.

There is a classical correspondence between edge-signed plane graphs and link diagrams. Determining component number of links corresponding to plane graphs may be one of the first problems in studying links by using graphs. There has been several early studies in this aspect, for example, the component number of links formed from 2-dimensional square lattices (44) has been determined. In this paper, we determine the component number of links corresponding to 2-dimensional triangular (36) and honeycomb (63) lattices with free or cyclic boundary condition.