diff --git a/2019-spring/Assignment-01.ipynb b/2019-spring/Assignment-01.ipynb
index f2ba971..68b7141 100644
--- a/2019-spring/Assignment-01.ipynb
+++ b/2019-spring/Assignment-01.ipynb
@@ -631,11 +631,19 @@
     "    if not rest: return (seg_pat, saying), len(saying)    \n",
     "    \n",
     "    for i, token in enumerate(saying):\n",
-    "        if rest[0] == token:  \n",
+    "        if rest[0] == token and is_match(rest[1:], saying[(i + 1):]):\n",
     "            return (seg_pat, saying[:i]), i\n",
     "    \n",
     "    return (seg_pat, saying), len(saying)\n",
-    "        "
+    "\n",
+    "def is_match(rest, saying):\n",
+    "    if not rest and not saying:\n",
+    "        return True\n",
+    "    if not all(a.isalpha() for a in rest[0]):\n",
+    "        return True\n",
+    "    if rest[0] != saying[0]:\n",
+    "        return False\n",
+    "    return is_match(rest[1:], saying[1:])"
    ]
   },
   {
@@ -988,7 +996,25 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.1"
+   "version": "3.7.0"
+  },
+  "latex_envs": {
+   "LaTeX_envs_menu_present": true,
+   "autoclose": false,
+   "autocomplete": true,
+   "bibliofile": "biblio.bib",
+   "cite_by": "apalike",
+   "current_citInitial": 1,
+   "eqLabelWithNumbers": true,
+   "eqNumInitial": 1,
+   "hotkeys": {
+    "equation": "Ctrl-E",
+    "itemize": "Ctrl-I"
+   },
+   "labels_anchors": false,
+   "latex_user_defs": false,
+   "report_style_numbering": false,
+   "user_envs_cfg": false
   }
  },
  "nbformat": 4,