Various examples of parasemifields Tomáš Kepka, Miroslav Korbelář (2009) Acta Universitatis Carolinae. Mathematica et Physica
Various subsemirings of the field ℚ of rational numbers Vítězslav Kala, Tomáš Kepka, Jon D. Phillips (2009) Acta Universitatis Carolinae. Mathematica et Physica