Self-dual gravity and self-dual Yang-Mills in the context of   Macdowell-Mansouri formalism
  In this work we propose an action which unifies self-dual gravity and self-dual Yang-Mills in the context of the Macdowell-Mansouri formalism. We claim that such an action may be used to find the S-dual action for both self-dual gravity and self-dual Yang-Mills. 
J.A. Nieto and J. Socorro