Barker, L.2019-02-142019-02-1419970025-5793http://hdl.handle.net/11693/49520Given a P-subgroup P of a finite group G, we express the number of P-blocks of G with defect group P as the /?-rank of a symmetric integer matrix indexed by the N (P) / P-conjugacy classes in PC(P)/P. We obtain a combinatorial criterion for P to be a defect group in G.EnglishArticle10.1112/S0025579300012687