Linking numbers, quandles and groups
Abstract
We introduce a quandle invariant of classical and virtual links, denoted by Qtc(L)Qtc(L). This quandle has the property that Qtc(L)≅Qtc(L′) if and only if the components of L and L′ can be indexed in such a way that L=K1∪⋯∪Kμ, L′=K′1∪⋯∪K′μ and for each index i, there is a multiplier 𝜖i∈{−1,1} that connects virtual linking numbers over Ki in L to virtual linking numbers over K′i in L′: ℓj/i(Ki,Kj)=𝜖iℓj/i(K′i,K′j) for all j≠i. We also extend to virtual links a classical theorem of Chen, which relates linking numbers to the nilpotent quotient G(L)/G(L)3.