Corollary
Tag 07WR, permanent. Cite it as [Bourbaki, Tag 07WR].
Topological Vector Spaces, chapter IV, Appendix 0. Fixed points of groups of affine transformations
— Let E be a reflexive Banach space, G a group of automorphisms of the normed space E, and K a subset of E. Suppose that K is non-empty, convex, closed, bounded and stable under G. Then there exists a point in K which is invariant under G.
Since E is reflexive, K is compact for (IV, p. 15, th. 1). Moreover, every element of G belongs to .
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.
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