© 1997 by London Mathematical Society
© The London Mathematical Society
Faithful Representations of Free Products
School of Mathematical Sciences, Queen Mary and Westfield College Mile End Road, London E1 4NS
Received 4 June 1995. Revision received 10 May 1996.
In 1940 Nisnevi
published the following theorem [3]. Let (G
)

be a family of groups indexed by some set
and (F
)

a family of fields of the same characteristic p
0. If for each
the group G
has a faithful representation of degree n over F
then the free product*

G
has a faithful representation of degree n+1 over some field of characteristic p. In [6] Wehrfritz extended this idea. If (G
)

GL(n, F) is a family of subgroups for which there exists Z
GL(n, F) such that for all
the intersection G
F.1n=Z, then the free product of the groups *ZG
with Z amalgamated via the identity map is isomorphic to a linear group of degree n over some purely transcendental extension of F.
Initially, the purpose of this paper was to generalize these results from the linear to the skew-linear case, that is, to groups isomorphic to subgroups of GL(n, D
) where the D
are division rings. In fact, many of the results can be generalized to rings which, although not necessarily commutative, contain no zero-divisors. We have the following.
Department of Mathematics and Computer Science, University of the West Indies, Mona Campus, Mona, Kingston 7, Jamaica