Definition#

Let \(\sim\) be an equivalence relation on a set \(S\). If \(a \in S\), then the equivalence class of \(a\), denoted \([a]\), is the set \(\{ b \in S : a \sim b \}\).

Source#

Gregory T. Lee. Abstract Algebra. 1st ed. Springer Cham, 2018. pp. 7.