reorders sp into a canonical order with respect to set.
ToCanonicalSetPartition[sp] reorders sp into canonical order, assuming that Mathematica knows the underlying order on the set for which sp is a set partition.
In the canonical order, the elements of each subset of the set partition are ordered as they appear in set, and the subsets themselves are ordered by their first elements.
, you first need to load the Combinatorica Package using 
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