A HashSet is an unordered collection of the unique elements. It comes under System.Collections.Generic namespace. It is used in a situation where we want to prevent duplicates from being inserted in the collection. As far as performance is concerned, it is better in comparison to the list. HashSet<T>.IsProperSubsetOf(IEnumerable<T>) method is used to check whether a HashSet<T> object is a proper subset of the specified collection.
Here, mySet1 and mySet2 are two HashSets.
Return Value: This method returns True if mySet1 is proper subset of mySet2 otherwise it returns false.
Exception: This method will give ArgumentNullException if the HashSets is null.
Below given are some examples to understand the implementation in a better way: