It is also
obvious that the difference between heights of any two students of the school has to be
less than 3 meters This shows that R′ = A × A is the universal relation Remark In Class XI, we have seen two ways of representing a relation, namely raster
method and set builder method However, a relation R in the set {1, 2, 3, 4} defined by R
= {(a, b) : b = a + 1} is also expressed as a R b if and only if
b = a + 1 by many authors