## Abstract

Let \(G\) be a bounded open subset of a Banach space \(X\) with \(0\in G\) and let \(f\) be a map from \(G\) into the dual \(X\). The following Krasnoselskii-Browder boundary inequality \( (x,f(x))\leq 0\) for all \( x\in \partial G\) is for some types of maps sufficient for the existence of solutions \(x\in G\) for equation \(f(x)=0\). This article deals with the reverse of the above inequality, namely \( (x,f(x))\leq 0 \) for all \( x \in \partial G\). We prove that if \(X\) is an infinite-dimensional Hilbert space, \(f=I-g\) where \(I\) is the identity on \(X\) and \(g: G\rightarrow X\) is completely continuous, then the inequality \((x,f(x))\leq 0\) can not be true for all \( x \in \partial G\). Consequently two existence theorems proved in [4] have no content since their assumptions are never satisfied. We then ask if such a negative result holds true even for more general maps of monotone type. A partial answer is finally given.

## Authors

## Keywords

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## Paper coordinates

R. Precup, *On the reverse of the Krasnoselskii-Browder boundary inequality*, Studia Univ. Babeş-Bolyai Math. 38 (1993) no. 2, 41-55.

## About this paper

##### Journal

Studia Universitatis Babes-Bolyai Mathematica

##### Publisher Name

Babeş-Bolyai University, Department of Mathematics, Cluj-Napoca, Romania

##### paper on journal website

##### Print ISSN

1221-8103

##### Online ISSN

2065-9490

ZB: 828.47055.

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## References

[1] Browder, F E , Fixed point-theory and nonlinear problems, Bull Amer Math Soc (New Series) 9(1983), 1-39

[2] Browder, F E , The theory of degree of mapping for nonlinear mappings of monotone type, Nonlinear Partial Differential Equations and Applications (H Brezis, J L Lions eds ) VI, Pitman, 1984,165-177

[3] Deimling, К , Nonlinear functional analysis, Springer, 1985

[4] Lakshimikantham, V , Sun, Yong, A theorem on the existence of two fixed points, Jour Math. Phy Sci 25(1991), 281-286

[5] Precup, R., Generalized topological transversality and mappings of monotone type. Studia Universitatis Babeş-Bolyai, Mathematica 35, No 2(1990), 44-50