On skein invariants

After J.H. Conway, it is known that some knot invariants can be defined by relations (called skein relations) on diagrams which differ at a local site. Among skein invariants one can mention Alexander and Jones polynomials, Arf invariant and writhe polynomial. In the talk we will remind these and other examples of skein invariants and introduce a new skein invariant for links in a fixed thickened surface.