Dooms, A., & Veloso, M. (2007). Normalizers and Free Groups in the Unit Group of an Integral Semigroup Ring. Journal of Algebra and Its Applications, 6, 655-669. http://www.worldscinet.com/cgi-bin/details.cgi?id=pii:S0219498807002429&type=html

@article{77d16ff4a6564399ab448325808c20d4,
title = "Normalizers and Free Groups in the Unit Group of an Integral Semigroup Ring",
abstract = "We constructed free groups in the unit group of an integral semigroup ring of a finite inverse semigroup using a bicyclic unit and its image under the natural involution.",
keywords = "free group, units, semigroup ring, normalizer",
author = "Ann Dooms and M. Veloso",
year = "2007",
month = aug,
day = "1",
language = "English",
volume = "6",
pages = "655--669",
journal = "Journal of Algebra and Its Applications",
issn = "0219-4988",
publisher = "World Scientific Publishing Co. Pte Ltd",
}