Usage:
<kernel_and_map f0 a b c g
Given f0, a, b making a commutative diagram
(where the vertical arrows go down):
C1 --> A1 --> B1
| | |
c | a| | b
| g | f0 |
C0 --> A0 --> B0
| | |
| | f |
ker f --> A --> B
we compute a presentation c for the kernel of f and
the comparison map g.
Parameters:
f0,a,b = matrices
Output values:
c,g = matrices
We first compute the relations on the generators
of the image of f0 modulo the image of b,
then a presentation of the kernel is obtained
by computing the relations on this
modulo the image of the map presenting a.