using System;
using System.Collections.Generic;
 
interface IX
{
    void X();
}
 
class XA : IX
{
    public void X() { Console.WriteLine("XA.X()"); }
}
 
static class XExtensions
{
    public static void X(this IEnumerable<IX> xList)
    {
        foreach (var x in xList)
        {
            x.X();
        }
    }
}
 
public class Program
{
    public static void Main(string[] args)
    {
        var xaArray = new[] { new XA() };
        xaArray.X();
    }
}
 

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