diff --git a/linked_lists/add_reverse/add_reverse_challenge.ipynb b/linked_lists/add_reverse/add_reverse_challenge.ipynb
index 345784a..d44c956 100644
--- a/linked_lists/add_reverse/add_reverse_challenge.ipynb
+++ b/linked_lists/add_reverse/add_reverse_challenge.ipynb
@@ -38,8 +38,8 @@
     "\n",
     "* Do you expect the return to be in reverse order too?\n",
     "    * Yes\n",
-    "* What if one of the inputs is NULL?\n",
-    "    * Return NULL for an invalid operation\n",
+    "* What if one of the inputs is None?\n",
+    "    * Return None for an invalid operation\n",
     "* How large are these numbers--can they fit in memory?\n",
     "    * Yes\n",
     "* Can we assume we already have a linked list class that can be used for this problem?\n",
diff --git a/linked_lists/add_reverse/add_reverse_solution.ipynb b/linked_lists/add_reverse/add_reverse_solution.ipynb
index 5d19963..e2db2a3 100644
--- a/linked_lists/add_reverse/add_reverse_solution.ipynb
+++ b/linked_lists/add_reverse/add_reverse_solution.ipynb
@@ -37,8 +37,8 @@
     "\n",
     "* Do you expect the return to be in reverse order too?\n",
     "    * Yes\n",
-    "* What if one of the inputs is NULL?\n",
-    "    * Return NULL for an invalid operation\n",
+    "* What if one of the inputs is None?\n",
+    "    * Return None for an invalid operation\n",
     "* How large are these numbers--can they fit in memory?\n",
     "    * Yes\n",
     "* Can we assume we already have a linked list class that can be used for this problem?\n",
@@ -73,17 +73,17 @@
     "    * if first and second lists are NULL AND carry is zero\n",
     "        * Return NULL\n",
     "* Recursive case:\n",
-    "    * value = carry\n",
-    "    * value += first.data + second.data\n",
-    "    * remainder = value % 10\n",
-    "    * new_carry = 1 if value >= 10, else 0\n",
-    "    * Create a node with the remainder\n",
-    "    * node.next = self.add(first.next, second.next, new_carry)\n",
-    "    * Return node\n",
+    "    * Set `value` to `carry`\n",
+    "    * Add both nodes' `data` to `value`\n",
+    "    * Set the `new_carry` to 1 if `value >= 10, else 0`\n",
+    "    * Set the `remainder` to `value % 10`\n",
+    "    * Create a `node` with the `remainder`\n",
+    "    * Set `node.next` to a recursive call on the `next` nodes, passing in the `carry`\n",
+    "    * Return `node`\n",
     "\n",
     "Complexity:\n",
     "* Time: O(n)\n",
-    "* Space: O(n), extra space for result and recursion depth\n",
+    "* Space: O(m), extra space for result and recursion depth\n",
     "\n",
     "Notes:\n",
     "* Careful with adding if the lists differ\n",
@@ -131,12 +131,12 @@
     "        value = carry\n",
     "        value += first_node.data if first_node is not None else 0\n",
     "        value += second_node.data if second_node is not None else 0\n",
-    "        remainder = value % 10\n",
     "        new_carry = 1 if value >= 10 else 0\n",
+    "        remainder = value % 10\n",
     "        node = Node(remainder)\n",
     "        node.next = self.__add_reverse__(first_node.next if first_node is not None else None, \n",
-    "                                     second_node.next if first_node is not None else None, \n",
-    "                                     new_carry)\n",
+    "                                         second_node.next if first_node is not None else None, \n",
+    "                                         new_carry)\n",
     "        return node\n",
     "\n",
     "    def add_reverse(self, first_list, second_list):\n",