A relation R is a non-empty sub-set of a cartesian product. A relation R is a non-empty sub-set of a cartesian product.
A relation is a set of ordered pairs, i.e., R Ì A x B where A and B are two non-empty sets. If R is a relation, write x R y or (x, y) 
R and we say x is R-related to y.
Iff x R y
Domain of a relation is the set of all first components.
Range of a relation is the set of all second components.
Examples:
a) "x is less than y"
b) " x is greater than y"c) "x is multiple of 3"
d) "x divides y"e) "Cube of x plus the square of y is 25"
f) "Triangle x is congruent to triangle y "
