An itemset X is called a closed itemset if there exists no proper superset Y of X with sup(X)=sup(Y) (here, "sup" denotes support). A closed itemset X is a top-k frequent closed itemset of minimal length min_l if there exists no more than (k-1) closed itemsets of length at least min_l whose support is higher than that of X. In this problem, we wish to mine top-k frequent closed itemsets of a given minimal length min_l in a transaction database.