Polynomials in (U, U)
12.1 Direct sums
In this section we develop some of the ideas from Section 5.4 which the reader may wish to reread. We start with some useful definitions.
Definition 12.1.1 Let U be a vector space over with subspaces Uj [1 ≤ j ≤ m].
(i) We say that U is the sum of the subspaces Uj and write
(ii) We say that U is the direct ...