The array implementation of multisets is really only practical if the number of items in the universe, N=|U|, is not too large. If N is large, then it is impractical, or at least extremely inefficient, to use an array of N counters to represent the multiset. This is especially so if the number of elements in the multisets is significantly less than N. If we use a linked list of elements to represent a multiset S, the space required is proportional to the size of the multiset, |S|. When the size of the multiset is significantly less than the size of the universe, tex2html_wrap_inline67534, it is more efficient in terms of both time and space to use a linked list.