[1] J. B. Conway,A course in functional analysis, Springer-Verlag, New York, 1990.
[2] D. Dubois and H. Prade,Gradual elements in a fuzzy set, Soft Computing-A Fusion of Foundations, Methodologies and Applications,12 (2007), 165-175.
[3] J. Fortin, D. Dubois and H. Prade,Gradual numbers and their application to fuzzy interval analysis, IEEE Transactions on Fuzzy Systems, 16 (2008), 388-402.
[4] U. Hoehle,Fuzzy real numbers as Dedekind cuts with respect to a multiple-valued logic, Fuzzy Sets and Systems,24 (1987), 263-278.
[5] E. Kaucher,Interval analysis in the extended interval space R, Computing Supplement,2(1980), 33-49.
[6] R. Lowen,Fuzzy set theory, Ch. 5 : Fuzzy Real Numbers, Kluwer, Dordrecht, 1996.
[7] S. E. Rodabaugh,Fuzzy addition in the L-fuzzy real line, Fuzzy Sets and Systems, 8 (1982),39-51.
[8] I. Sadeqi and M. Salehi,Fuzzy compact operators and topological degree theory, Fuzzy Sets and Systems,160 (2009), 1277-1285.