Ordered Sets and Lattices 8-3
Example 4 The relation of divisibility over the set of integers Z is not a partial order relation.
Solution: a/b and b/a do not imply a = b and hence the relation is not antisymmetric.
For example, 5/−5 and −5/5 ⇒/ 5 = −5.
Example 5 The relation < (less than) over Z
+
is not a partial order relation.
Solution: The relation ‘less than’ is not reflexive and hence is not a partial order relation.
Note 8.1 The relation ≥ ‘greater than or equal to’ is a partial order relation over the set of real
numbers. If R is a partial order relation on a set A, then R
−1
, the inverse relation of R is also a
partial order relation on A. The POSET (A, R
−1
) is called Dual POSET of (A, R). The inverse of
symbol ≤ is denoted by ≤
-1