code: func (deque *keyedDeque) Push(key interface{}, val interface{}) {
  	deque.Lock()
  	defer deque.Unlock()
  
  	if e, ok := deque.index[key]; ok {
  		deque.syncedList.Remove(e)
  	}
  	deque.index[key] = deque.syncedList.PushBack(val)
  	deque.invertedIndex[deque.index[key]] = key
  }
docs: // Push pushs a keyed-value to the end of deque.