# relation

A relation from set  to set is a subset of their Cartesian product, . A relation between two sets is also called a binary relation. Relations between more than two sets are called n-ary relations.

More formally, a binary relation is defined as an ordered triple: . is the domain of the relation, is the codomain, and is the subset of , also known as the relation’s graph.

Since by definition is a set of ordered pairs , then for all ordered pairs where and , one, and only one of the following must be true:

• ; this is read “a is R-related to b” and is written .
• ; this is read “a is not R-related to b” and is written .

Some properties of binary relations:

• reflexive
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