     "file_extension": ".py",
     "mimetype": "text/x-python",
     "name": "python",
     "nbconvert_exporter": "python",
     "pygments_lexer": "ipython2",
     "version": "2.7.10"
    }
   },
   "nbformat": 4,
   "nbformat_minor": 0
  }
 
</s> remove    "pygments_lexer": "ipython2",
   "version": "2.7.10"
 </s> add    "pygments_lexer": "ipython3",
   "version": "3.5.0" </s> remove    "pygments_lexer": "ipython2",
   "version": "2.7.10"
 </s> add    "pygments_lexer": "ipython3",
   "version": "3.5.0" </s> remove    "pygments_lexer": "ipython2",
   "version": "2.7.10"
 </s> add    "pygments_lexer": "ipython3",
   "version": "3.5.0" </s> remove     "version": 2
 </s> add     "version": 3 </s> remove     "version": 2
 </s> add     "version": 3
   "pygments_lexer": "ipython3",
   "version": "3.5.0"
     "file_extension": ".py",
     "mimetype": "text/x-python",
     "name": "python",
     "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.5.0"
   "pygments_lexer": "ipython3",
   "version": "3.5.0"
    }
   },
   "nbformat": 4,
   "nbformat_minor": 0
  }
keep keep keep keep replace replace keep keep keep keep keep
 Update constraints for bfs and dfs graph challenge and solution (#88) 
graphs_trees/graph_bfs/bfs_challenge.ipynb