This object maps each key to a Set of values and holds each member of this
Set as a link to a Set of keys, i.e., depicts a IMultiMap (object -> set)
with an inverse IMultiMap.
This object maps each key to a Set of values and holds each member of this
Set as a link to a Set of keys, i.e., depicts a IMultiMap (object -> set)
with an inverse IMultiMap.