Iranian Mathematical Society (IMS) Bulletin of the Iranian Mathematical Society 1017-060X 27 No. 2 2001 01 24 Schur-Pair Property and the Structure of Varietal Covering Groups1 16 en A. R. Salemkar M. R. R. Moghaddam 1998 11 11 Variety of groups Baer-invariant Schur-pair V-isologism V-covering group V-perfect group