As multiset is similar to set except that it allows
duplicate elements, multimap is similar to map except that
it allows for duplicate keys. Like multiset (Multiset),
accessing ranges of pair objects is done by using
lower_bound and upper_bound. The search operations
available for set are also available to multimap, so we'll
not look at them here because the interface is exactly the same. Just be
aware that since you'd do a search on (for example)
lower_bound(key), that you'll have to get the key from the
pair object representing the multimaps element using the
first member of pair. Like map, you use a multimap
in your code by including <map>.