Relation

A relation is any Subset of a Cartesian Product. For instance, a Subset of $A \times B$, called a (binary) ``relation from $A$ to $B$,'' is a collection of Ordered Pairs $(a,b)$ with first components from $A$ and second components from $B$, and, in particular, a Subset of $A \times A$ is called a ``relation on $A$.'' For a binary relation $R$, one often writes $a R b$ to mean that $(a,b)$ is in $R$.

See also Adjacency Relation, Antisymmetric Relation, Argument Addition Relation, Argument Multiplication Relation, Cover Relation, Equivalence Relation, Irreflexive, Partial Order, Recurrence Relation, Reflection Relation, Reflexive Relation, Symmetric Relation, Transitive, Translation Relation