General comments on multiplying chain maps.

Let L be a chain map of degree d.
Then L is represented as a list 
having in position 1 a map P_d -> P_0,
in position 2 a map P_{d+1} -> P_1, etc.
such that the standard diagram commutes.

Let M be a chain map of degree e.
Observe that in position e+1, L has a
map P_{e+d} -> P_e.

Therefore, the product of M*L has
L[e+1] * M[1] in position 1
L[e+2] * M[2] in position 2, etc.

However, since L and M are represented
as lists of non-lifted matricies, we have
to lift the matrix on the right using
LiftHom. So M*L actually has
L[e+1] * LiftHom(...,M[1],...) in position 1,
L[e+2] * LiftHom(...,M[2],...) in position 2, etc.
The result is non-lifted because the
matrix on the left is non-lifted.

