diff --git a/graphs_trees/graph_path_exists/path_exists_challenge.ipynb b/graphs_trees/graph_path_exists/path_exists_challenge.ipynb
index 95d1250..cc21f3f 100644
--- a/graphs_trees/graph_path_exists/path_exists_challenge.ipynb
+++ b/graphs_trees/graph_path_exists/path_exists_challenge.ipynb
@@ -37,6 +37,10 @@
     "* Is the graph directed?\n",
     "    * Yes\n",
     "* Can we assume we already have Graph and Node classes?\n",
+    "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -177,21 +181,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,
diff --git a/graphs_trees/graph_path_exists/path_exists_solution.ipynb b/graphs_trees/graph_path_exists/path_exists_solution.ipynb
index 378d046..a37d4b7 100644
--- a/graphs_trees/graph_path_exists/path_exists_solution.ipynb
+++ b/graphs_trees/graph_path_exists/path_exists_solution.ipynb
@@ -36,6 +36,10 @@
     "* Is the graph directed?\n",
     "    * Yes\n",
     "* Can we assume we already have Graph and Node classes?\n",
+    "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -130,8 +134,6 @@
     "    start.visit_state = State.visited\n",
     "    while queue:\n",
     "        node = queue.popleft()\n",
-    "        if node is None:\n",
-    "            continue\n",
     "        if node is end:\n",
     "            return True\n",
     "        for adj_node in node.adjacent:\n",
@@ -222,21 +224,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,