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A relation R is defined b/w two elements. Hence elements in a relation are oddered pairs; the relation R from a non empty set A to a non empty set B is a subset of AXB ie R c AXB Note A relation R from A to B is denoted by R:A_B All relations from A to B are subsets of AXB If (a,b)ER,then be say that a is related to under the relation B . And we write aRb A relation R in the set A is denoted by R from A to A . Which is a subset of AXA Let R:A_B be a relation and n(A) =P and n(B)=q, then number of relations from A to B is given by 2n(AXB)=2n(A).n(B)=2pq DOMAIN AND RANGE OF A RELATION ; Let R from A_ B is a relation . Then the set of all first elements in R called domain, the set of all second element in R is called range of R and second set B is called co-domain of R TYPES OF RELATION 1) EMPTY RELATION . A relation R in the set A is called an empty relation . If no element in A is related to any element in A