The main features
of this chapter are as follows:
®
Empty relation is the relation R in X given by R = φ ⊂ X × X ®
Universal relation is the relation R in X given by R = X × X ®
Reflexive relation R in X is a relation with (a, a) ∈ R ∀ a ∈ X ®
Symmetric relation R in X is a relation satisfying (a, b) ∈ R implies (b, a) ∈ R