Transitive relation

Equivalence relation

Equivalence class

Reflexive relation

R in X is a relation satisfying (a, b) ∈ R and (b, c) ∈ R implies that (a, c) ∈ R.

R in X is a relation which is reflexive, symmetric and transitive

a ∈ X for an equivalence relation R in X is the subset of X containing all elements b related to a.

(a, a) ∈ R ∀ a ∈ X