      "    * Return None for an invalid operation\n",
      "* How large are these numbers--can they fit in memory?\n",
      "    * Yes\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
      "    * Yes"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s>
    "    * Yes\n",
    "* Can we assume this fits in memory?\n",
      "    * Return None for an invalid operation\n",
      "* How large are these numbers--can they fit in memory?\n",
      "    * Yes\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
    "    * Yes\n",
    "* Can we assume this fits in memory?\n",
      "    * Yes"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep keep keep add keep keep keep keep keep keep
 Update linked list constraints

Specify singly linked list, non circular.  Also specify the solution fits in memory.
linked_lists/add_reverse/add_reverse_challenge.ipynb