Central extensions of reductive groups by K 2 Jean-Luc Brylinski, Pierre Deligne (2001) Publications Mathématiques de l'IHÉS
Extensions centrales de groupes algébriques simplement connexes et cohomologie galoisienne Pierre Deligne (1996) Publications Mathématiques de l'IHÉS
On irreducible projective representations of finite groups. Costache, Tania-Luminiţa (2009) Surveys in Mathematics and its Applications
The Schur multiplier of a generalized Baumslag-Solitar group Derek J. S. Robinson (2011) Rendiconti del Seminario Matematico della Università di Padova