diff --git a/tasks/04 - neuron.ipynb b/tasks/04 - neuron.ipynb
index dadfbaf..9d50def 100644
--- a/tasks/04 - neuron.ipynb	
+++ b/tasks/04 - neuron.ipynb	
@@ -19,11 +19,13 @@
    "outputs": [],
    "source": [
     "def sigmoid(z):\n",
-    "    return 1/ (1+ e** (-z))\n",
+    "    return 1 / (1 + e ** (-z))\n",
+    "\n",
     "\n",
     "def ht(weights, x):\n",
     "    return g(weights.T @ x)\n",
     "\n",
+    "\n",
     "def g(x):\n",
     "    return sigmoid(x)"
    ]
@@ -48,10 +50,10 @@
     "# and gate?\n",
     "weights_and = np.array([-30, 20, 20])\n",
     "\n",
-    "print(ht(weights_and, np.array([1,1,1])))\n",
-    "print(ht(weights_and, np.array([1,0,1])))\n",
-    "print(ht(weights_and, np.array([1,0,0])))\n",
-    "print(ht(weights_and, np.array([1,1,0])))\n"
+    "print(ht(weights_and, np.array([1, 1, 1])))\n",
+    "print(ht(weights_and, np.array([1, 0, 1])))\n",
+    "print(ht(weights_and, np.array([1, 0, 0])))\n",
+    "print(ht(weights_and, np.array([1, 1, 0])))\n"
    ]
   },
   {
@@ -74,10 +76,10 @@
     "# not x and not y gate?\n",
     "weights = np.array([10, -20, -20])\n",
     "\n",
-    "print(ht(weights, np.array([1,1,1])))\n",
-    "print(ht(weights, np.array([1,0,1])))\n",
-    "print(ht(weights, np.array([1,0,0])))\n",
-    "print(ht(weights, np.array([1,1,0])))\n"
+    "print(ht(weights, np.array([1, 1, 1])))\n",
+    "print(ht(weights, np.array([1, 0, 1])))\n",
+    "print(ht(weights, np.array([1, 0, 0])))\n",
+    "print(ht(weights, np.array([1, 1, 0])))\n"
    ]
   },
   {
@@ -99,10 +101,10 @@
    "source": [
     "# or gate?\n",
     "weights = np.array([-10, 20, 20])\n",
-    "print(ht(weights, np.array([1,1,1])))\n",
-    "print(ht(weights, np.array([1,0,1])))\n",
-    "print(ht(weights, np.array([1,0,0])))\n",
-    "print(ht(weights, np.array([1,1,0])))\n"
+    "print(ht(weights, np.array([1, 1, 1])))\n",
+    "print(ht(weights, np.array([1, 0, 1])))\n",
+    "print(ht(weights, np.array([1, 0, 0])))\n",
+    "print(ht(weights, np.array([1, 1, 0])))\n"
    ]
   },
   {
@@ -113,7 +115,7 @@
    "source": [
     "# make it more generic\n",
     "def layer(a: array, w: array, debug=False) -> array:\n",
-    "    a_with_one: array = np.concatenate(([1],a))\n",
+    "    a_with_one: array = np.concatenate(([1], a))\n",
     "    z = w @ a_with_one\n",
     "    a_next = sigmoid(z)\n",
     "\n",
@@ -139,10 +141,49 @@
    "source": [
     "# or gate but cooler\n",
     "weights = np.array([1, -10, 20, 20])\n",
-    "print(layer(np.array([1,1,1]),weights  ))\n",
-    "print(layer(np.array([1,0,1]),weights  ))\n",
-    "print(layer(np.array([1,0,0]),weights  ))\n",
-    "print(layer(np.array([1,1,0]),weights  ))\n"
+    "print(layer(np.array([1, 1, 1]), weights))\n",
+    "print(layer(np.array([1, 0, 1]), weights))\n",
+    "print(layer(np.array([1, 0, 0]), weights))\n",
+    "print(layer(np.array([1, 1, 0]), weights))\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 58,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "0.9999545869652744\n",
+      "4.5622486386054965e-05\n",
+      "4.5622486386054965e-05\n",
+      "0.9999545869652744\n"
+     ]
+    }
+   ],
+   "source": [
+    "# xnor gate, needs 3 layers\n",
+    "weights = [\n",
+    "    np.array(\n",
+    "        [\n",
+    "            [1, -30, 20, 20],\n",
+    "            [1, 10, -20, -20],\n",
+    "        ]\n",
+    "    ),\n",
+    "    np.array([-10, 20, 20]),\n",
+    "]\n",
+    "\n",
+    "def l2(x: array, w1: array, w2: array) -> array:\n",
+    "    z = layer(x, w1)\n",
+    "    z2 = layer(z, w2)\n",
+    "    return z2\n",
+    "\n",
+    "print(l2(np.array([1,0,0]), weights[0], weights[1]))\n",
+    "print(l2(np.array([1,1,0]), weights[0], weights[1]))\n",
+    "print(l2(np.array([1,0,1]), weights[0], weights[1]))\n",
+    "print(l2(np.array([1,1,1]), weights[0], weights[1]))"
    ]
   }
  ],