A Banach space A Banach space X such that all its closed subspaces are complemented.

******************************

Any Hilbert space.
Note that Lindenstrauss and Tzafriri, showed that each Banach space for which every closed subspace is complemented is isomorphic to a Hilbert space (cf. [J. Lindenstrauss and L. Tzafiriri, On complemented subspaces problem. Israel J. Math., 2, 1984, 375-378].)

File translated from TEX by TTH, version 2.70.
On 22 Feb 2001, 00:16.