Hopefully this java can illustrate the point if you're not a Java lover The bag essentially works like this Map<K, Collection<V>> But looks like this Bag<K, V

Hopefully this java can illustrate the point if you're not a Java lover The bag essentially works like this Map<K, Collection<V>> But looks like this Bag<K, V> I use my own simple "BagSet" which works like this Map<K, Set<V>>