1. Brink, C., Britz, K., Schmidt, R.A.: Peirce algebras. Formal Aspects Comput. 6(3), 339–358 (1994)
2. Fokkinga M.: A Summary of Refinement Theory., : Unregistered Technical Report. University of Twente, Enschede, Netherlands (1994)
3. Goldblatt R.: Topoi: The Categorial Analysis of Logic. North- Holland (1984)
4. Järvinen, J.: Knowledge Representation and Rough Sets. Ph.D. Dissertation, University of Turku (1999)
5. Lawvere, F.W.: Adjointness in foundations. Dialectica 23(3/4), 281–296 (1969)