Let H be a group. We mean by an Af-series in H a decreasing series of subgroups H1 = H, H2…,Hn+1 = {e} such that the commutator xyx-1y-1 of two elements x and y respectively in Hi and Hj belongs to Hi+j, where Hs = {e} for s≥n + 1. We call n the length of the N-series (Hi). We mean by a graded Lie ring of length n a Lie ring which is a direct sum A1 + … + -An of additive subgroups A1…, An such that [Ai, Aj]⊂Ai+j, where As = {0} for s≥n + 1.