Bourbaki's Fixpoint Lemma reconsidered
Bernhard Banaschewski · Czech digital mathematics library · 1992
summary:A constructively valid counterpart to Bourbaki's Fixpoint Lemma for chain-complete partially ordered sets is presented to obtain a condition for one closure system in a complete lattice $L$ to be stable under another closure operator of $L$. This is then used to deal with coproducts and other aspects of frames.