@Override
  public boolean equals(Object obj)
  { if(obj instanceof Set)
    { Set that=(Set)obj;
      if(this.size()!=that.size())
      { return false;
      }
      else
      { for(Set<T> p=that;p!=null;p=p.next)
        { if(!this.hasElement(p.a))
          { return false;
          }
          else
          { continue;
          }  
        } 
        return true;
      }    
    }
    else
    { return false;
    }  
  }