using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
public static void Main() {
int[] seq1 = { 1, 2, 3 };
int[] seq2 = { 3, 4, 5 };
IEnumerable concat = seq1.Concat(seq2); // { 1, 2, 3, 3, 4, 5 }
IEnumerable union = seq1.Union(seq2); // { 1, 2, 3, 4, 5 }
}
}