CHR(G, p, [F], [mats] )
CHR constructs a cohomology-record, which is used as a parameter for
all of the other functions in this chapter. G must be a finite
permutation group, and p a prime number. If present, F must either be
zero or a finitely presented group with the same number of generators as
G, of which the relators are satisfied by the generators of G.
In fact, to obtain meaningful results, F should almost certainly be
isomorphic to G. If present, mats should be a list of invertible matrices
over the finite field K = GF(p). The list should have the same length as the
number of generators of G, and the matrices should correspond to these
generators, and define a GF(p)G-module, which we will denote by M.
GAP 3.4.4