public static void Main()
var list1 = new[] { 1, 1, 2 };
var list2 = new[] { 1, 2, 3 };
var unioned = list1.Union(list2);
var distinct = list1.Concat(list2).Distinct();
Console.WriteLine("unioned: " + string.Join(",", unioned.Select(x => x.ToString()).ToArray()));
Console.WriteLine("distinct: " + string.Join(",", distinct.Select(x => x.ToString()).ToArray()));