namespace OxyPlot.WindowsForms {

   using System;

   using System.Collections.Generic;

   using System.Text;

   public class HashSet<T> {

     private readonly Dictionary<T, object> set = new Dictionary<T, object>();

     public bool Add(T value) {

       if (set.ContainsKey(value))

         return true;

       set.Add(value, null);

       return false;

     }

     public bool Contains(T value) {

       return set.ContainsKey(value);

     }

     public void Clear() {

       set.Clear();

     }

   }

 }