  Given a formal power series f(z) we define, for any positive integer r, its
rth Witt transform, W_f^{(r)}, by rW_f^{(r)}(z)=sum_{d|r}mu(d)f(z^d)^{r/d},
where mu is the Moebius function. The Witt transform generalizes the necklace
polynomials M(a,n) that occur in the cyclotomic identity
  1-ay=prod (1-y^n)^{M(a,n)}, where the product is over all positive integers.
  Several properties of the Witt transform are established. Some examples
relevant to number theory are considered.
