A number of classical theorems of ring theory deal with nilness and nilpotency of the Jacobson radical of various ring constructions (see [10], [18] This paper is devoted to the radicals of group graded rings, which have been actively investigated by many authors (see [10], [14]). Let G be a group. An associative ring R = 0 ^g is said to be G-graded {stronglyFirst, we consider algebras over a field of characteristic zero. In this case our result will be also of interest in connection with the well-known problem of finding necessary and sufficient conditions for the Jacobson radical to be homogeneous. An ideal / of R = 0 R g is said to be homogeneous if / = 0 IC\R g . This problem has not been solved
Pi-algebra over a field of characteristic zero. If the Jacobson radical J(R e ) is nil, then J(R) is a homogeneous nil ideal of R.The following corollary to the main theorem is worth mentioning.COROLLARY 2. Let G be a group with identity e, and let R = 0 R g be a strongly g &G
G-graded Pi-algebra over a field of characteristic zero. IfJ(R e ) is nilpotent, then J(R) is nilpotent.It is impossible to replace strongly graded algebras by ordinary group graded algebras in Corollary 2. Indeed, let A be the free commutative algebra with free generators a u a 2 , Denote by / the ideal of A generated by a u a\, a\, Then All is positively graded, and so All = 0 A z where Z is the infinite cyclic group. Although A o = 0, it is zeZ clear that J(A/I) = A/1 is not nilpotent.One cannot omit the restriction on the characteristic of the field neither in Theorem Glasgow Math.