hom_and_map

Usage:
    <hom_and_map a b c ff
The module Hom(a,b) is put into the
variable c. ff is set to the map inducing
the natural map Hom(A,b) --> Hom(A0,b),
where
                    a
    A1 --> A0 --> A --> 0
s the given presentation.
Parameters:
            a,b = modules
Output values:
            c = Hom(a,b)
This script is used in the script
double_dual1, where the map
A --> Hom(Hom(A,B),B) is computed.
We will compute Hom as the kernel of
the map
               f = Hom(a,B)
            Hom(A0,B)  ------------>  Hom(A1,B), where
where b is a presentation of B and
        a
            A1 --> A0
is a.