/// <summary>
/// Determines whether the current set is a proper (strict) subset of a specified collection.
/// </summary>
/// <param name="other">The collection to compare to the current set.</param>
/// <returns>true if the current set is a correct subset of other; otherwise, false.</returns>
public bool IsProperSubsetOf(IEnumerable <T> other)
{
return(ImmutableHashSet <T> .IsProperSubsetOf(other, this.Origin));
}
