## Description

`C**D` -- the tensor product of two chain complexes.

The result, `E`, is a chain complex. Each module `E_k` in it is a direct sum of modules of the form `C_i**D_j` with `i+j=k`, and the preferred keys for the components of this direct sum are the pairs `(i,j)`, sorted increasing values of `i`. For information about how to use preferred keys, see directSum.