标题： 核心组 显示英文标题

标题： Core groups

摘要： 经典链的核群是由A.J. Kelly于1991年和M. Wada于1992年分别独立引入的。它是一个通过链图的弧和交叉点定义的链不变量，与链补集的基本群的Wirtinger表示有关。核群的两个密切相关的定义是通过涉及区域而非弧的表示来定义的；其中一个与Dehn的链群表示有关。这些定义被扩展到虚拟链图，并讨论了由此产生的不变量的性质。 显示英文摘要

摘要： The core group of a classical link was introduced independently by A.J. Kelly in 1991 and M. Wada in 1992. It is a link invariant defined by a presentation involving the arcs and crossings of a diagram, related to Wirtinger's presentation of the fundamental group of a link complement. Two close relatives of the core group are defined by presentations involving regions rather than arcs; one of them is related to Dehn's presentation of a link group. The definitions are extended to virtual link diagrams and properties of the resulting invariants are discussed.