     ]
    },
    {
     "cell_type": "code",
     "execution_count": 8,
     "metadata": {
      "collapsed": false
     },
     "outputs": [],
     "source": [
 
</s> remove    "execution_count": 14,
 </s> add    "execution_count": null, </s> remove    "execution_count": 3,
 </s> add    "execution_count": null, </s> remove   },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
 </s> add  </s> remove    "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Dequeue on empty stack\n",
      "None\n",
      "Enqueue on empty stack\n",
      "Enqueue on non-empty stack\n",
      "Multiple enqueue in a row\n",
      "Dequeue on non-empty stack\n",
      "Dequeue after an enqueue\n",
      "0\n",
      "Multiple dequeue in a row\n",
      "1\n",
      "2\n",
      "Enqueue after a dequeue\n",
      "5\n",
      "None\n"
     ]
    }
   ],
 </s> add    "outputs": [], </s> remove     "        if self.is_stack_empty(self.right_stack) and not self.is_stack_empty(self.left_stack):\n",
 </s> add     "        if self.right_stack.is_empty() and not self.left_stack.is_empty():\n",
   "execution_count": null,
     ]
    },
    {
     "cell_type": "code",
   "execution_count": null,
     "metadata": {
      "collapsed": false
     },
     "outputs": [],
     "source": [
keep keep keep keep replace keep keep keep keep keep
 Updated problem solution to use stack's is_empty() method rather than a similar method that used to be in QueueFromStacks. 
stacks-queues/queue-from-stacks.ipynb