Model structures for homotopy of internal categories. Everaert, T., Kieboom, R.W., Van der Linden, T. (2005) Theory and Applications of Categories [electronic only]
More about homological properties of precrossed modules. Inassaridze, Nick, Khmaladze, Emzar (2000) Homology, Homotopy and Applications
More about the (co)homology of groups and associative algebras. Inassaridze, Hvedri (2005) Homology, Homotopy and Applications