diff --git a/stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb b/stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb
index f476670..e65df05 100644
--- a/stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb
+++ b/stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb
@@ -136,6 +136,9 @@
     "    def is_full(self):\n",
     "        return self.num_items == self.capacity\n",
     "\n",
+    "    def is_empty(self):\n",
+    "        return self.num_items == 0\n",
+    "\n",
     "\n",
     "class SetOfStacks(object):\n",
     "\n",
@@ -154,10 +157,9 @@
     "        if self.last_stack is None:\n",
     "            return None\n",
     "        data = self.last_stack.pop()\n",
-    "        if not self.last_stack.num_items:\n",
+    "        if self.last_stack.is_empty():\n",
     "            self.stacks.pop()\n",
-    "            self.last_stack = self.stacks[-1] \\\n",
-    "                if len(self.stacks) else None\n",
+    "            self.last_stack = self.stacks[-1] if self.stacks else None\n",
     "        return data"
    ]
   },