Binary Relations
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چکیده
The notion of a relation between two sets of objects is quite common and intuitively clear. Let X be the set of all living human females and Y the set of all living human males. The wife-husband relation R can be defined from X to Y . Thus, if x ∈ X and y ∈ Y , then x is related to y by the relation R if x is a wife of y, and we write xRy. To describe the relation R, we may take the collection of all ordered pairs (x, y) such that x is related to y by R; the collection of related ordered pairs is simply a subset of the product set X × Y . This motivates the definition of relations.
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