1. Z. Arad, D. Chillag and G. Moran, Groups with a small covering number, Chapter 4 of this book.
2. J.L. Brenner, M. Randall and J. Riddell, Covering theorems for FINASIGS, I, Colloq. Math. 32 (1974), 39–48.
3. J.L. Brenner, Covering theorems for FINASIGS, II, J. Comb. Theorye 14 (1973), 264–269.
4. J.L. Brenner and L. Carlitz, Covering theorems for FINASIGS, III, Rend. Seminario Mat. di Padova 55 (1974), 81–90.
5. J.L. Brenner, Covering theorems for FINASIGS, IV, Jñānabha, Section A, 3 (1975), 77–84.