Sets invariant under projections onto two dimensional subspaces
نویسندگان
چکیده
The Blaschke–Kakutani result characterizes inner product spaces E, among normed spaces of dimension at least 3, by the property that for every 2 dimensional subspace F there is a norm 1 linear projection onto F . In this paper, we determine which closed neighborhoods B of zero in a real locally convex space E of dimension at least 3 have the property that for every 2 dimensional subspace F there is a continuous linear projection P onto F with P (B) ⊆ B.
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