Published online by Cambridge University Press: 20 November 2018
By a group ring we mean in this paper a ring defined by a finite group G and an integral domain K:
such that A contains G and is freely generated by G over K, so that
The ring A = KG has a co-multiplication
defined by
so that A is a Hopf algebra.
1) In particular J. L. Kelley, Duality for compact groups, Proc. N. A. S. 49 (1963) pp. 457-458.
*) The author would like to thank Professor Geoffrey Fox and the referee for their valuable suggestions.
2) We follow the presentation of S. MacLane, Homology, 1963, pp. 197-198.
3) Always commutative with the identity 1.