Abstract
This paper proposes a formally stronger set-valued Caristi's fixed point theorem and by using a simple method we give a direct proof for the equivalence between Ekeland's variational principle and this set-valued Caristi's fixed point theorem. The results stated in this paper improve and strengthen the corresponding results in [4].
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References
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Caristi, J., Fixed point theorems for mappings satisfying inwardness conditions,Trans. Amer. Math. Soc.,215 (1976), 241–251.
Shi Shu-zhong, The equivalence between Ekeland's variational principle and Caristi's fixed point theorem,Advan. Math.,16, 2 (1987), 203–206. (in Chinese)
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Shi-shen, Z., Qun, L. Set-valued Caristi's fixed point theorem and Ekfland's variational principle. Appl Math Mech 10, 119–121 (1989). https://doi.org/10.1007/BF02014818
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DOI: https://doi.org/10.1007/BF02014818