1. Algebra of Programming;Bird,1997
2. Categories, Allegories;Freyd,1990
3. H. Furusawa, Algebraic formalisations of fuzzy relations and their representation theorems, Ph.D. Thesis, Kyushu University, 1998.
4. L-fuzzy sets;Goguen;J. Math. Anal. Appl.,1967
5. P.T. Johnstone, Sketches of an Elephant, A Topos Theory Compendium, vol. 1, Oxford Logic Guides, vol. 42, 2002.