Duality for the sl₂ weight system

The sl₂ weight system, corresponding to the colored Jones polynomial of knots, is one of the the simplest weight system for chord diagrams. Recent works have led to explicit computations of this weight system on chord diagrams with complete and complete bipartite intersection graphs using sl₂ weight systems on shares, i.e., on chord diagrams on two strands. In this paper, we continue our study of shares. We prove a conjecture by Lando about a duality of values of the sl₂ weight system on chord diagrams whose intersection graphs are joins of complementary graphs with discrete ones. To achieve this, we introduce the two-colored intersection graph of shares, define the inner product of shares, and use chord-adding operators.