hi all .

I have a problem with my code in C# . if i click in compiler button , I get the following errors

'System.Collections.Generic.LinkedList' does not contain a definition for 'removeFirst' and no extension method 'removeFirst' accepting a first argument of type 'System.Collections.Generic.LinkedList' could be found (are you missing a using directive or an assembly reference?).

and

'System.Collections.Generic.LinkedList' does not contain a definition for 'addLast' and no extension method 'addLast' accepting a first argument of type 'System.Collections.Generic.LinkedList' could be found (are you missing a using directive or an assembly reference?)

This is part of a simple program

using System;

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

namespace Hanoi
{
   public class Sol
    {

public LinkedList<int?> t1 = new LinkedList<int?>();
   public LinkedList<int?> t2 =new LinkedList<int?>();
   public LinkedList<int?> t3 =new LinkedList<int?>();
   public int depth;

   public LinkedList<Sol> neighbors;

    public Sol(LinkedList<int?> t1, LinkedList<int?> t2, LinkedList<int?> t3)
    {
        this.t1 = t1;
        this.t2 = t2;
        this.t3 = t3;

        neighbors = new LinkedList<Sol>();
    }

    public virtual void getneighbors()
    {

        Sol temp = this.copy();
        Sol neighbor1 = this.copy();
        Sol neighbor2 = this.copy();
        Sol neighbor3 = this.copy();
        Sol neighbor4 = this.copy();
        Sol neighbor5 = this.copy();
        Sol neighbor6 = this.copy();





        if (temp.t1.Count != 0)
        {

            if (neighbor1.t2.Count != 0)
            {
                if (neighbor1.t1.First.Value < neighbor1.t2.First.Value)
                {
                    neighbor1.t2.AddFirst(neighbor1.t1.RemoveFirst());
                    neighbors.AddLast(neighbor1);
                }

            }
            else
            {
                neighbor1.t2.AddFirst(neighbor1.t1.RemoveFirst());
                neighbors.AddLast(neighbor1);
            }



            if (neighbor2.t3.Count != 0)
            {
                if (neighbor2.t1.First.Value < neighbor2.t3.First.Value)
                {
                    neighbor2.t3.AddFirst(neighbor2.t1.RemoveFirst());
                    neighbors.AddLast(neighbor2);
                }
            }
            else

I hope that you find someone to help me