The subgroup determined by a certain ideal in a free group ring

Abstract

For normal subgroups R and S of a free group F, an identification of the subgroup F∩(1+rfs) is derived, and it is shown that the quotient. F∩(1+rfs)[R'∩S',R∩S][R'∩S,R'∩S][R∩S',R∩S'] is, in general, non-trivial.