An equivalence relation on a set is a Subset of , i.e., a collection of ordered pairs of elements of , satisfying certain properties. Write ``'' to mean is an element of , and we say `` is related to ,'' then the properties are
See also Equivalence Class, Teichmüller Space
Stewart, I. and Tall, D. The Foundations of Mathematics. Oxford, England: Oxford University Press, 1977.