On closeness of the sum of n subspaces of a Hilbert space
Abstract
We give necessary and sufficient conditions for the sum of subspaces $H_1,..., H_n,, \quad n \geq 2,$ of a Hilbert space $H$ to be a subspace and present various properties of $n$-tuples of subspaces with closed sum.
English version (Springer): Ukrainian Mathematical Journal 63 (2011), no. 10, pp 1566-1622.
Citation Example: Feshchenko I. S. On closeness of the sum of n subspaces of a Hilbert space // Ukr. Mat. Zh. - 2011. - 63, № 10. - pp. 1381-1425.
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