1. R. Baire. Leçons sur les fonctions discontinues, professées au collège de France. Gauthier-Villars, Paris, 1905.
2. R. N. Ball, J. Walters-Wayland. C- and C
∗-quotients in pointfree topology. Dissertationes Mathematicae (Rozprawy Mat.) 412 (2002) 1–62.
3. B. Banaschewski. σ-frames. Unpublished manuscript, 1980.
4. B. Banaschewski. Compactifications of frames. Math. Nachr. 149 (1990) 105–115.
5. B. Banaschewski. The Real Numbers in Pointfree Topology. Textos de Matemática, vol. 12. University of Coimbra, 1997.