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Mathematical logic and foundations Definition

Ordered pair

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Definition

An ordered pair (a,b)(a, b) has a first entry aa and a second entry bb, with this property: (a,b)=(c,d)  ⟺  a=c and b=d.(a, b) = (c, d) \iff a = c \text{ and } b = d. In set theory, the Kuratowski definition is (a,b)={{a},{a,b}}(a, b) = \{\{a\}, \{a, b\}\}. It has the property above.

Remarks

In general (a,b)≠(b,a)(a, b) \neq (b, a), but the sets {a,b}\{a, b\} and {b,a}\{b, a\} are equal. Ordered pairs are the elements of a Cartesian product. An ordered triple can be defined as (a,b,c)=((a,b),c)(a, b, c) = ((a, b), c).

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Further reading

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