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For equal-size subsets $A$ and $B$ of an ordered ground set, $A$ precedes $B$ in lexicographic order when the smallest element of their symmetric difference belongs to $A$.

For finite sequences over a total order, lexicographic order compares the first differing sequence terms; the smaller term determines the smaller sequence. If one sequence is a proper prefix of the other, the shorter precedes its extension. For fixed-length tuples, this is the first-difference rule used by radix sort key encoding.