The Hurkens article i alluded to earlier (containing a nice proof
that the relation ``the power set of x injects into y'' is
wellfounded is
A.C.J Hurkens. The relation $\pow x \cap y)$ is wellfounded. Collegium Logicum, Annals of the Kurt G\"odel Soc. {\bf 4} (1999) pp 244$-$6
Thomas Forster