Published online by Cambridge University Press: 20 January 2009
Dieudonné (4) has constructed an example of a Banach space X and a complete Boolean algebra of projections on X such that
has uniform multiplicity two, but for no choice of x1, x2 in X and non-zero E in
is EX the direct sum of the cyclic subspaces clm {Ex1:E∈
} and clm {Ex2:E∈
}. Tzafriri observed that it could be deduced from Corollary 4 (9, p. 221) that the commutant
′ of
is equal to A(
), the algebra of operators generated by
in the uniform operator topology. A study of (3) suggested the direct proof of the second property given in this note. From this there follows a simple proof that
has the first property.