Owl_utils_multimap.MakeSourcemodule Ord : Map.OrderedTypeType of a multimap.
``mem k m`` returns true is the multimap ``m`` contains at least one binding for ``k``, false otherwise.
``add k v m`` returns a multimap containing the same bindings as ``m``, plus a binding from ``k`` to ``v``. Previous bindings for ``k`` are hidden by the new binding (they can be restored by calling ``remove k m``).
``remove k v m`` returns a multimap with the same bindings as ``m``, except for the binding of ``k``: the last value that was bound to it is removed. If there is no binding for ``k`` in ``m``, raises `Not_found`.
``find k m`` returns the last added binding of ``k`` in ``m``, or raises ``Not_found`` if there is no such binding.
``max_binding m`` returns the greatest binding in ``m``. Raises ``Not_found`` if ``m`` is empty.