**Unit 18 Exercises**

**1. **List the ordered pairs in the relation *R* from
*A = *{0,1, 2, 3} to *B *= {0, 1, 2, 3, 4} where *(a, b) *
*R* if and only if

*a > b.**a + b = 3.**a*divides*b.**a - b = 0.*- gcd(
*a*,*b*) =*1.* - lcm(
*a*,*b*) =*6.*

**2. **Recursively define the relation { (*a*,
*b*) | *a=2b* }, where *a* and
*b* are natural numbers.

**3. **List unary relation on {1, 2, 3}.

**4. **Prove that there are *2 ^{n2}*
binary relations on a set of cardinality