      "* Space: O(m), extra space for result and recursion depth\n",
      "\n",
      "Notes:\n",
      "* Careful with adding if the lists differ\n",
      "    * Only add if a node is not NULL\n",
      "    * Alternatively, we could add trailing zeroes to the smaller list"
     ]
    },
    {
     "cell_type": "markdown",
 
</s> remove     "    * if first and second lists are NULL AND carry is zero\n",
    "        * Return NULL\n",
 </s> add     "    * if first and second lists are None AND carry is zero\n",
    "        * Return None\n", </s> remove     "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with a NULL value?\n",
 </s> add     "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with value None?\n", </s> remove     "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with a NULL value?\n",
 </s> add     "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with value None?\n", </s> remove     "* If data we are deleting is NULL, return\n",
 </s> add     "* If data we are deleting is None, return\n", </s> remove     "* If the data we are inserting is NULL, return\n",
 </s> add     "* If the data we are inserting is None, return\n",
    "    * Only add if a node is not None\n",
      "* Space: O(m), extra space for result and recursion depth\n",
      "\n",
      "Notes:\n",
      "* Careful with adding if the lists differ\n",
    "    * Only add if a node is not None\n",
      "    * Alternatively, we could add trailing zeroes to the smaller list"
     ]
    },
    {
     "cell_type": "markdown",
keep keep keep keep replace keep keep keep keep keep
 Changed discussions of NULL to None to be more Pythonic. 
linked_lists/add_reverse/add_reverse_solution.ipynb