diff --git a/ipynb/Advent 2017.ipynb b/ipynb/Advent 2017.ipynb
index b6a1215..96d5420 100644
--- a/ipynb/Advent 2017.ipynb	
+++ b/ipynb/Advent 2017.ipynb	
@@ -2511,7 +2511,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 70,
+   "execution_count": 125,
    "metadata": {},
    "outputs": [
     {
@@ -2529,7 +2529,8 @@
     "    d = perform(dance, d)\n",
     "    if d in seen:\n",
     "        print(d, 'is seen in iterations', (seen[d], i))\n",
-    "        break"
+    "        break\n",
+    "    seen[d] = i"
    ]
   },
   {
@@ -4016,7 +4017,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The `numba.jit` decorator really helps here, speeding up execution from 13 seconds to 1 second. It also helped on Day 15, but not as dramatically, and was not able to help on Day 22.\n",
+    "The `numba.jit` decorator really helps here, speeding up execution from 13 seconds to 1 second. It also helped on Day 15, but not as dramatically, and was not able to help on Day 15 or Day 22.\n",
     "\n",
     "\n",
     "# [Day 24](https://adventofcode.com/2017/day/24): Electromagnetic Moat\n",
@@ -4193,7 +4194,7 @@
     "        for c in ctable[port] - chain:\n",
     "            # Update chain, port, strength\n",
     "            # then recurse and possibly update best_strength\n",
-    "            # then backtrack and rest chain, port, strength\n",
+    "            # then backtrack and restore chain, port, strength\n",
     "            chain.add(c)\n",
     "            port = other_port(c, port)\n",
     "            strength += sum(c)\n",
@@ -4220,7 +4221,7 @@
    "source": [
     "# [Day 25](https://adventofcode.com/2017/day/25): The Halting Problem\n",
     "\n",
-    "I won't write a parser for my input; instead I'll translate it into a `dict`:"
+    "I won't write a parser for my input; instead I'll translate it into a `dict` by hand:"
    ]
   },
   {
@@ -4235,13 +4236,12 @@
     "    \"machine()[state][value] == (new_value, move, new_state)}\"\n",
     "    L, R = -1, +1\n",
     "    A, B, C, D, E, F = 'ABCDEF'\n",
-    "    return {\n",
-    "        A: ((1, R, B), (0, L, C)),\n",
-    "        B: ((1, L, A), (1, R, D)),\n",
-    "        C: ((0, L, B), (0, L, E)),\n",
-    "        D: ((1, R, A), (0, R, B)),\n",
-    "        E: ((1, L, F), (1, L, C)),\n",
-    "        F: ((1, R, D), (1, R, A))}"
+    "    return {A: ((1, R, B), (0, L, C)),\n",
+    "            B: ((1, L, A), (1, R, D)),\n",
+    "            C: ((0, L, B), (0, L, E)),\n",
+    "            D: ((1, R, A), (0, R, B)),\n",
+    "            E: ((1, L, F), (1, L, C)),\n",
+    "            F: ((1, R, D), (1, R, A))}"
    ]
   },
   {
@@ -4268,7 +4268,7 @@
     }
    ],
    "source": [
-    "def turing(machine, state='A', steps=12667664):\n",
+    "def turing(machine, state, steps):\n",
     "    \"Run the Turing machine for given number of steps, then return tape.\"\n",
     "    tape = defaultdict(int)\n",
     "    cursor = 0\n",
@@ -4277,7 +4277,36 @@
     "        cursor += move\n",
     "    return tape\n",
     "\n",
-    "sum(turing(machine()).values())"
+    "sum(turing(machine(), 'A', 12667664).values())"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 128,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "4770"
+      ]
+     },
+     "execution_count": 128,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "def turing(machine, state):\n",
+    "    \"Run the Turing machine, starting at state; yield tape each step.\"\n",
+    "    tape = defaultdict(int)\n",
+    "    cursor = 0\n",
+    "    while True:\n",
+    "        tape[cursor], move, state = machine[state][tape[cursor]]\n",
+    "        cursor += move\n",
+    "        yield tape\n",
+    "\n",
+    "quantify(nth(turing(machine(), 'A'), 12667664).values())"
    ]
   },
   {
@@ -4397,7 +4426,7 @@
     "             run23_2() == 913,\n",
     " 24: lambda: strongest_chain() == 1695 and\n",
     "             strength(max(chains(), key=length_and_strength)) == 1673,\n",
-    " 25: lambda: sum(turing(machine()).values()) == 4769\n",
+    " 25: lambda: quantify(nth(turing(machine(), 'A'), 12667664).values()) == 4769\n",
     "})"
    ]
   },