What is the Kuratowski Definition of an Ordered Pair in Set Notation?

In summary, the Kuratowski definition of the ordered pair is a set-theoretic representation of an object with the property that (a,b) = (c,d) if and only if a=c and b=d. This definition allows for the notion of order to be captured, as shown by the example of {{a},{a,b}} and {{b}, {b,a}} being distinct sets. The actual representation of ordered pairs is not important, as long as it satisfies the desired properties.
  • #1
Gear300
1,213
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The Kuratowski definition of the ordered pair is (a,b) = {{a},{a,b}}...this sort of lost me...how did they define an ordered pair (in which order of elements matters) using set notation (how does this definition work)?
 
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  • #2
An ordered pair (a,b) is supposed to be some object with this property:

(a,b) = (c,d) if and only if a=c and b=d.

What it actually *is* we don't care, as long as it has this property. Kuratowski wrote down his definition as something that has this property.
 
  • #3
g_edgar said:
An ordered pair (a,b) is supposed to be some object with this property:

(a,b) = (c,d) if and only if a=c and b=d.

What it actually *is* we don't care, as long as it has this property. Kuratowski wrote down his definition as something that has this property.

I see...I thought they were defining (a,b) with the expression. So, in that sense, the expression does not show that order matters, right?
 
  • #4
Gear300 said:
I see...I thought they were defining (a,b) with the expression. So, in that sense, the expression does not show that order matters, right?

Yes it does. Notice that if a is not equal to b, the RHS becomes {{b}, {b,a}} which is definitely not equal to {{a}, {a,b}}. Also, if {{a}, {a,b}} = {{x}, {x,y}}, then necessarily a = x and b = y.

This is just a way of capturing the notion of ordered pairs with a set-theoretic definition. What ordered pairs actually are, like g_edgar said, doesn't really matter: as long your notion/definition of them has the desired properties, then there is no harm done.
 
  • #5
I see...Thanks for the replies...but isn't {{a},{a,b}} just another way of writing {a,b}?
 
  • #6
Gear300 said:
I see...Thanks for the replies...but isn't {{a},{a,b}} just another way of writing {a,b}?

No... {a,b} is not the same as {{a}, {a,b}}. The members of the first set are a and b, the members of the second are {a} and {a,b}. The members of the second set are NOT a and b, if this is what you are implying.
 
  • #7
Gear300 said:
I see...Thanks for the replies...but isn't {{a},{a,b}} just another way of writing {a,b}?
{1,3} is the same as {3,1}. But {{1},{1,3}} is not the same as {{3},{3,1}}. Kuratowski's definition basically states that there are two elements and distinguishes between the two, thus giving an order.
 
  • #8
Thus, the elements are different...I think I see what's going on to a better extent. Thanks for the replies.
 

Related to What is the Kuratowski Definition of an Ordered Pair in Set Notation?

1. What is an ordered pair?

An ordered pair is a set of two objects or elements in a specific order. The first element is usually referred to as the x-coordinate and the second element as the y-coordinate. It is denoted as (x,y).

2. What is the difference between an ordered pair and an unordered pair?

The main difference between an ordered pair and an unordered pair is the specific order in which the elements are listed. In an unordered pair, the order of the elements does not matter, while in an ordered pair, the order is important and changes the meaning of the pair. For example, the ordered pair (1,2) is different from the ordered pair (2,1).

3. How is an ordered pair used in mathematics?

An ordered pair is used in mathematics to represent the coordinates of a point on a coordinate plane. It is also used to represent the domain and range of a function, where the first element represents the input value (x-coordinate) and the second element represents the output value (y-coordinate).

4. Can an ordered pair have duplicate elements?

No, an ordered pair cannot have duplicate elements. Each element in an ordered pair must be unique and cannot be repeated. This is because the order of the elements is important and changes the meaning of the pair.

5. What is the difference between a Cartesian product and an ordered pair?

A Cartesian product is the set of all possible ordered pairs that can be formed by combining elements from two sets. An ordered pair, on the other hand, is a specific set of two elements in a defined order. In other words, a Cartesian product is a collection of ordered pairs, while an ordered pair is a specific type of pair.

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