The adjunction between crossed modules and precrossed modules over a fixed group can be seen as a special case of a more general adjunction between internal groupoids and internal reflexive graphs in a Mal'tsev variety. By using the categorical Galois theory, we characterize the central extensions with respect to this latter adjunction in terms of the universal algebraic commutator. In particular, we get a description of the central extensions of precrossed modules and of precrossed rings. This characterization provides a natural way to define a categorical notion of Peiffer commutator. (c) 2005 Elsevier Inc. All rights reserved.
Everaert, T., & Gran, M. (2006). Precrossed modules and Galois theory. Journal of Algebra, 297(1), 292-309. https://doi.org/10.1016/j.jalgebra.2005.06.034 (Original work published 2006)