Factoring out free fields

For a generic $\Ww$ algebra, we give an algorithmic procedure for factoring out all fields of dimension $1/2$, both bosonic and fermionic, and some fields of dimension $1$. This generalizes and makes more explicit the Goddard-Schwimmer theorem for free fermions. We also show how the induced gravity theory for the original $\Ww$ algebra containing the free fields relates to the theory where the fields are factored out.