On models in the alternative set theory Michal Resl (1979) Commentationes Mathematicae Universitatis Carolinae
On the Continuity of Internal Functions Hermann Render (1993) Publications de l'Institut Mathématique
On the paracompactness of frames Xiangdong Chen (1992) Commentationes Mathematicae Universitatis Carolinae Through the study of frame congruences, new characterizations of the paracompactness of frames are obtained.