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In mathematics, an ordered pair ( a, b ) is a pair of mathematical objects.

In the ordered pair ( a, b ), the object a is called the first entry, and the object b the second entry of the pair.

Alternatively, the objects are called the first and second coordinates, or the left and right projections of the ordered pair.

The order in which the objects appear in the pair is significant: the ordered pair ( a, b ) is different from the ordered pair ( b, a ) unless a = b.