     "mimetype": "text/x-python",
     "name": "python",
     "nbconvert_exporter": "python",
     "pygments_lexer": "ipython3",
     "version": "3.4.3"
    }
   },
   "nbformat": 4,
   "nbformat_minor": 0
  }
 
</s> remove    "version": "3.4.3"
 </s> add    "version": "3.5.0" </s> remove     "If the `root` input is `None`, return a tree with the only element being the new root node."
 </s> add     "If the `root` input is `None`, return a tree with the only element being the new root node.\n",
    "\n",
    "You do not have to code the in-order traversal, it is part of the unit test." </s> remove     "If the `root` input is `None`, return a tree with the only element being the new root node."
 </s> add     "If the `root` input is `None`, return a tree with the only element being the new root node.\n",
    "\n",
    "You do not have to code the in-order traversal, it is part of the unit test." </s> remove     "### In-Order Traversal (Provided)\n",
 </s> add     "### In-Order Traversal\n", </s> remove     "### In-Order Traversal (Provided)\n",
 </s> add     "### In-Order Traversal\n",
   "version": "3.5.0"
     "mimetype": "text/x-python",
     "name": "python",
     "nbconvert_exporter": "python",
     "pygments_lexer": "ipython3",
   "version": "3.5.0"
    }
   },
   "nbformat": 4,
   "nbformat_minor": 0
  }
keep keep keep keep replace keep keep keep keep keep
 Polish bst challenge and solution (#75)

Update constraints, algorithm discussion, and code. 
graphs_trees/bst/bst_challenge.ipynb