SMITH, Jonathan D.H. Quasigroups and loops : theory and applications. Berlin : Heldermann Verlag, c1990. xii, 568 s. Sigma series in pure mathematics ; Vol. 8. Dostupné na internetu: <http://www.gbv.de/dms/hbz/toc/ht003664584.pdf> ISBN 3-88538-008-0.