An ordering for the Cartesian product of any two sets and with order relations and , respectively, such that if and both belong to , then iff either

1. ,
or

2.
and .

The lexicographic order can be readily extended to cartesian products of arbitrary length by recursively applying this definition, i.e., by observing that .

When applied to permutations, lexicographic order is increasing numerical order (or equivalently, alphabetic order for lists of symbols;
Skiena 1990, p. 4). For example, the permutations
of
in lexicographic order are 123, 132, 213, 231, 312, and 321.

When applied to subsets, two subsets are ordered by their smallest elements (Skiena 1990, p. 44). For example, the subsets of in lexicographic order are , , , , , , , .

Lexicographic order is sometimes called dictionary order.