We prove the following result: Let X be a real Hilbert space and let J: X → ℝ be a C¹ functional with a nonexpansive derivative. Then, for each r > 0, the following alternative holds: either J’ has a fixed point with norm less than r, or .
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-sm211-2-3, author = {Biagio Ricceri}, title = {Another fixed point theorem for nonexpansive potential operators}, journal = {Studia Mathematica}, volume = {209}, year = {2012}, pages = {147-151}, zbl = {1269.47043}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm211-2-3} }
Biagio Ricceri. Another fixed point theorem for nonexpansive potential operators. Studia Mathematica, Tome 209 (2012) pp. 147-151. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm211-2-3/