Comment.Math.Univ.Carolin. 33,2 (1992)303–309 303 Bourbaki’s Fixpoint Lemma reconsidered

Abstract. 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