  Empirical analysis of many colored knot polynomials, made possible by recent
computational advances in Chern-Simons theory, reveals their stability: for any
given negative N and any given knot the set of coefficients of the polynomial
in r-th symmetric representation does not change with r, if it is large enough.
This fact reflects the non-trivial and previously unknown properties of the
differential expansion, and it turns out that from this point of view there are
universality classes of knots, characterized by a single integer, which we call
defect, and which is in fact related to the power of Alexander polynomial.
