We have found that in certain cases, branches of the candidate itemset tree can be "pruned" away, leading to fewer itemsets that need to be checked, and therefore a faster running time. This section explains what each of these pruning steps do.
Parent Equivalence Pruning- If an itemset in the tree has the same support as one of its candidate extensions, then it can be pruned from the tree because it must only occur in the database as part of that candidate extension.
HUTMFI Superset Pruning- If the union of an itemset and its leftmost tail on the ordered subtree is frequent then the entire subtree can be pruned away. This process checks the current list of maximal frequent itemsets to see if this head-union-tail is already on this list.
FHUT- Frequent Head-Union-Tail- This pruning method is identical to HUTMFI except it actually checks the support of the HUT rather than searching to see if it is already in the MFI list. FHUT has been found to yield fewer performance increases than HUTMFI.