Intersect

 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] seq1 = { 1, 2, 3 };
        int[] seq2 = { 3, 4, 5 };

        IEnumerable<int> commonality = seq1.Intersect(seq2);

        foreach (int i in commonality)
        {
            Console.WriteLine(i);
        }
    }
}