Description: Define the class of subcomplex modules, which are left modules over a
subring of the field of complex numbers CCfld , which allows to use
the complex addition, multiplication, etc. in theorems about subcomplex
modules. Since the field of complex numbers is commutative and so are
its subrings (see subrgcrng ), left modules over such subrings are the
same as right modules, see rmodislmod . Therefore, we drop the word
"left" from "subcomplex left module". (Contributed by Mario Carneiro, 16-Oct-2015)