Chapter 2 Sums and quotients

  • Convention. In this chapter, all vector spaces are over the same field \(\F \) unless we say otherwise.

2.1 Sums of subspaces

  • Definition. Let \(\lst {V}1k\leq V\). The sum \(\plst {V}1k\) is the set

    \begin{equation*} \plst {V}1k:=\set {\plst {v}1k\st v_i\in V_i, 1\leq i\leq k}. \end{equation*}

  • Proposition 2.1. Let \(\lst {V}1k\leq V\). Then

    • (1) \(\plst {V}1k\leq V\).

    • (2) If \(W\leq V\) and \(\lst {V}1k\leq W\) then \(\lst {V}1k\leq \plst {V}1k\leq W\).