we say that T is reducible. Conceivably we must distinguish between Qand Z-reducibility of a Z-representation. This difficulty does not in fact arise, because of the following theorem due to Zassenhaus [3 ]. (A) An integral representation is Q-reducible if and only if it is Z-reducible. It is well-known that any given Q-representation T of G is Qequivalent to a completely reduced representation