diff --git a/notebooks/problem0009.ipynb b/notebooks/problem0009.ipynb
index 22860b6..e61cdb1 100644
--- a/notebooks/problem0009.ipynb
+++ b/notebooks/problem0009.ipynb
@@ -30,7 +30,7 @@
     "def primitive_pythagorean_triplets():\n",
     "    for m in count(2):\n",
     "        for n in range(1, m):\n",
-    "            if not ((m % 2) != (n % 2)) or gcd(m, n) != 1:\n",
+    "            if ((m % 2) == (n % 2)) or gcd(m, n) != 1:\n",
     "                continue\n",
     "\n",
     "            a = m ** 2 - n ** 2\n",