set difference

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set difference The dyadic operation between two sets S and T, say, resulting in the set S T consisting of those elements that are in S but not in T. Formally ST = {s | sS and sT}

Set difference is a generalization of the idea of the complement of a set and as such is sometimes called the relative complement of T with respect to S. The symmetric difference between two sets S and T is the union of S T and T S.