The minimal number of edges required to form a knot or link of type K is the edge number of K, and is denoted e(K). When knots are drawn with edges, they are appropriately called piecewise-linear or PL knots. This paper presents some edge number results for PL knots. Included are illustrations of and integer coordinates for the vertices of several prime PL knots.
Those maps of a closed surface to the three-dimensional torus that are homotopic to embeddings are characterized. Particular attention is paid to the more involved case when the surface is nonorientable.
Soit un enlacement de intervalles dans d’extérieur et soit . On utilise la propriété de la paire d’être -acyclique pour certaines représentation de l’anneau du groupe fondamental de dans un anneau pour construire des invariants de torsion à valeurs dans le groupe . Un cas particulier est le polynôme d’Alexander en variables quand est l’anneau des fractions rationnelles avec et est simplement l’abélianisation.
For any link and for any modulus m we introduce an equivalence relation on the set of non-trivial m-colorings of the link (an m-coloring has values in Z/mZ). Given a diagram of the link, the equivalence class of a non-trivial m-coloring is formed by each assignment of colors to the arcs of the diagram that is obtained from the former coloring by a permutation of the colors in the arcs which preserves the coloring condition at each crossing. This requirement implies topological invariance of the...