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A distance formula related to a family of projections orthogonal to their symmetries
Let u be a hermitian involution, and e an orthogonal projection, acting on
the same Hilbert space. We establish the exact formula, in terms of the norm of
eue, for the distance from e to the set of all orthogonal projections q from
the algebra generated by e,u, and such that quq=0.Comment: 6 pages, 1 figur
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