Expressing infinite matrices as sums of idempotents

Abstract

Let $\scr M_{Cf} (F)$ be the set of all column-finite $N \times N$ matrices over a field $F$. The following problem is studied: what elements of $\scr M_{Cf} (F)$ can be expressed as a sum of idempotents? The result states that every element of $\scr M_{Cf} (F)$ can be represented as the sum of 14 idempotents.