1. Fixed point theorems for mappings satisfying inwardness conditions;Caristi;Trans. Amer. Math. Soc.,1976
2. Fixed degree for fuzzy mappings and generalization of Fan's theorem;Chang;Fuzzy Sets and Systems,1987
3. A general ordering and fixed point principle in complete metric spaces;Dancs;Acta Sci. Math.,1983
4. On the variational principle;Ekland;J. Math. Anal. Appl.,1974
5. On fixed points in partially ordered sets and Kirk-Caristi theorem;Kashara;Math. Seminar Notes, Kobe Univ.,1975