Davvaz, Bijan. "A Short Note on Bands of Groups." Journal of the Indonesian Mathematical Society, vol. 21, no. 1, Apr. 2015, pp. 19-23.
In this paper we give necessary and sufficient conditions on a semigroup S that it be semilattice of groups, a normal band of groups, and a matrix of groups.DOI : http://dx.doi.org/10.22342/jims.22.214.171.124-23