using System;

using System.Collections.Generic;

​

public class Example

{

    public static void Main()

    {

        var firstSet = new HashSet<string>( new string[] { "SQL", "Java", "C#", "PHP" });

        var secondSet = new HashSet<string>( new string[] { "Oracle", "SQL", "MySQL" });

        var union = new HashSet<string>(firstSet);

        union.UnionWith(secondSet);

        PrintSet(union);

    }

​

    public static void PrintSet<T>(ISet<T> set)

    {

        foreach (var element in set)

        {

            Console.Write("{0} ", element);

        }

​

        Console.WriteLine();

    }

}