example of antisymmetric
The axioms of a partial ordering demonstrate that every partial ordering is antisymmetric. That is: the relation on a set forces
and implies
for every .
For a concrete example consider the natural numbers (as defined by the Peano postulates (http://planetmath.org/PeanoArithmetic)). Take the relation set to be:
Then we denote if . That is, because and both .
We can prove this relation is antisymmetric as follows: Suppose and for some . Then there exist such that and . Therefore
so by the cancellation property of the natural numbers, . But by the first piano postulate, 0 has no predecessor, meaning unless .