internal void                        LeaveList(tIndexedList list)
 {
     this.changedKeyListeners.Remove(list.onKeyChanged);
     this.changingKeyListeners.Remove(list.onKeyChanging);
 }
 internal void                        JoinList(tIndexedList list)
 {
     this.changedKeyListeners.Add(list.onKeyChanged);
     this.changingKeyListeners.Add(list.onKeyChanging);
 }