Question

In: Advanced Math

Define d to be the set of all pairs (x,y) of natural numbers such that x...

Define d to be the set of all pairs (x,y) of natural numbers such that x divides y. Show that N is partially ordered by d. Define d analogously on Z. Is then d also a partial order on Z?

Expert Solution

Given

So, is a relation over the set of all natural numbers. We have to show that is partially ordered by , that is, is a partial order relation on the set .

1. Every number divides itself, so

Hence the relation d is reflexive.

2. Let

that is, a divides b, and, b divides c, that is

Clearly, this implies that a divides c

Thus,

Therefore the relation d is transitive.

3. Now, let

That is, a divides b, and, b divides a. As a,b are natural numbers, this is only possible when they are equal. Hence

Therefore, the relation is antisymmetric.

Thus, from 1,2, and 3, we can say that is a partial order relation on .

However, this does not hold true when the underlying set changes to , the set of all integers. In this case, antisymmetry fails, because we can have numbers such as:-

such that

and

but clearly,

Hence, d fails to be a partial order on Z.

Colby Messinger answered 2 years ago

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