1. On mathematical systems theory;Albrecht,1998
2. Topological theory of fuzziness;Albrecht,1999
3. Lattice Theory;Birkhoff,1967
4. N. Bourbaki, Topologie Générale, Hermann & Cie, Paris, 1951 (Chapitre I, II).
5. Metric Spaces of Fuzzy Sets, Theory and Applications;Diamond,1994