     "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     "In: 4  Out: 5\n",
    "In: 5  Out: 6\n",
    "In: 8  Out: 9\n",
    "In: 15 Out: None\n",
 </s> add     "In: None  Out: Exception\n",
    "In: 4     Out: 5\n",
    "In: 5     Out: 6\n",
    "In: 8     Out: 9\n",
    "In: 15    Out: None\n", </s> remove     "In: 4  Out: 5\n",
    "In: 5  Out: 6\n",
    "In: 8  Out: 9\n",
    "In: 15 Out: None\n",
 </s> add     "In: None  Out: Exception\n",
    "In: 4     Out: 5\n",
    "In: 5     Out: 6\n",
    "In: 8     Out: 9\n",
    "In: 15    Out: None\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 successor challenge and solution (#82)

Update constraints, test cases, tests, algorithm discussion, and code. 
graphs_trees/bst_successor/bst_successor_challenge.ipynb