We show that the special Schreier extensions of monoids, with abelian kernel, admit a Baer sum construction, which generalizes the classical one for group extensions with abelian kernel. In order to do that, we characterize the special Schreier extensions by means of factor sets.
Martins-Ferreira, N., Montoli, A., & Sobral, M. (2016). Baer sums of special Schreier extensions of monoids. Semigroup Forum. Accepted/in-press. https://doi.org/10.1007/s00233-016-9780-2 (Original work published 2016)