@ARTICLE{PittsAM:newffcff,
 AUTHOR={R.~L.~Crole and A.~M.~Pitts},
 TITLE={New Foundations for Fixpoint Computations:
 FIX-hyperdoctrines and the FIX-logic},
 JOURNAL={Information and Computation},
 VOLUME=98,
 YEAR=1992,
 PAGES={171--210}}