Perspectives of differential expansion

We outline the current status of the differential expansion (DE) of colored knot polynomials i.e. of their Z–F decomposition into representation– and knot–dependent parts. Its existence is a theorem for HOMFLY-PT polynomials in symmetric and antisymmetric representations, but everything beyond is still hypothetical – and quite difficult to explore and interpret. However, DE remains one of the main sources of knowledge and calculational means in modern knot theory. We concentrate on the following subjects: applicability of DE to non-trivial knots, its modifications for knots with non-vanishing defects and DE for non-rectangular representations. An essential novelty is the analysis of a more-naive Z–FTw decomposition with the twist-knot F-factors and non-standard Z-factors and a discovery of still another triangular and universal transformation V, which converts Z to the standard Z-factors V−1Z=Z and allows to calculate F as F=VFTw.