A relation is a set of tuples, all of which have the same
arity. The inclusion of a tuple in a relation indicates that the components of the tuple are related. A set of -tuples is called an -ary relation. Sets of pairs are called binary relations, sets of triples are called ternary relations, etc.Examples of binary relations include the equality relation on natural numbers and the predecessor relation . When a symbol is used to denote a specific binary relation ( is commonly used for this purpose), that symbol can be used with infix notation to denote set membership: means that the pair is an element of the set .