getall                  Get all permutation/combination for a iterator
getcurrent              Get the current element of a iterator
getlength               Get the length for a iterator
getnext                 Get the next permutation(s)/combination(s) for
                        a iterator
iterpc                  Iterator for Permutations and Combinations
multichoose             Calculate mulinomial coefficient
nc_multiset             Calcuate the number of combinations of a
                        multiset
np_multiset             Calcuate the number of r-permutations of a
                        multiset
