@article {MR1830043,
	title = {On generators and relations for unions of semigroups},
	journal = {Semigroup Forum},
	volume = {63},
	number = {1},
	year = {2001},
	pages = {49{\textendash}62},
	issn = {0037-1912},
	author = {Ara{\'u}jo, Isabel M. and Branco, M{\'a}rio J. J. and Fernandes, Vitor H. and Gomes, Gracinda M. S. and Ru{\v s}kuc, N.}
}
