Unit sum numbers of modules
If M is a module over the ring R, then the set of R–endomorphisms of M form a ring
ER(M). We shall say that the module M has the n–sum property or has the unit sum
number k if the ring ER(M) has the corresponding property.
It follows immediately from Proposition 1.2(c) that a free R–module of finite rank has
the n–sum property if R has; in particular a finite dimensional vector space over a field
F = GF(2) has unit sum number equal to 2. Indeed finite dimensional vector spaces
over GF(2) have the same property, with one exception, as established below.