We thank Y. Mellier and L. Van Waerbeke for fruitful discussions. We are also very grateful to B. Jain, U. Seljak and S. White for the use of their ray-tracing simulations and to K. Reblinsky for providing us with some of the data published in Reblinsky et al. (1999).
© European Southern Observatory (ESO) 2000
Online publication: December 15, 2000