An Implementation of Regular Expression Parser in C#

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

namespace RegularExpression
{
  /// <summary>
  /// this class represent a Set in Mathmatics, nothing else.
  /// Since .NET does not have any built-in class for Set, I decided to create one myself.
  /// Since this programm does many Set opertions, this class will help writing clean code
  /// Many of the methods of this class have not been used in this program.
  /// </summary>
  public class Set : CollectionBase
  {
    public object this[int index]
    {
      get
      {
        return ((object)List[index]);
      }
      set
      {
        List[index] = value;
      }
    }

    public int AddElement(object element)
    {
      if (Contains(element) == false)
      {
        return List.Add(element);
      }
      return -1;
    }

    public void AddElementRange(object[] arrValue)
    {
      foreach (object obj in arrValue)
      {
        if (Contains(obj) == false)
        {
          List.Add(obj);
        }
      }
    }

    public void Union(Set setValue)
    {
      foreach (object obj in setValue)
      {
        if (Contains(obj) == false)
        {
          List.Add(obj);
        }
      }
    }

    public bool IsSubset(Set setValue)
    {
      foreach (object obj in setValue)
      {
        if (Contains(obj) == false)
        {
          return false;
        }
      }
      return true;
    }

    public bool IsProperSubset(Set setValue)
    {
      if (GetCardinality() > setValue.GetCardinality() && IsSubset(setValue) )
      {
        return true;
      }

      return false;

    }

    public void Subtract(Set setValue)
    {
      foreach (object obj in setValue)
      {
        if (Contains(obj) == true)
        {
          RemoveElement(obj);
        }
      }
    }

    public bool IsEqual(Set setValue)
    {
      if (GetCardinality() == setValue.GetCardinality() && IsSubset(setValue))
      {
        return true;
      }

      return false;

    }

    public bool IsEmpty()
    {
      return List.Count == 0 ? true : false;
    }

    public int GetCardinality()
    {
      return List.Count;
    }

    public bool ElementExist(object value)
    {
      return Contains(value);
    }

    public int IndexOf(object value)
    {
      return (List.IndexOf(value));
    }

    public bool RemoveElement(object value)
    {
      if (Contains(value) == true)
      {
        List.Remove(value);
        return true;
      }

      return false;

    }

    private bool Contains(object value)
    {
      // If value is not of type Int16, this will return false.
      return List.Contains(value);
    }
    
    protected override void OnInsert(int index, object value)
    {
      if (value == null)
      {
        throw new ArgumentException("Element cannot not be null.");
      }

      if (Contains(value) == true )
      {
        throw new ArgumentException("Element already exists in the set.", "value: " + value.ToString());
      }

      

    }

    public Array ToArray(Type type)
    {
      return base.InnerList.ToArray(type);
    }


  }
}