add reference to Danny's lecture on lists

Author: Rise Riyo

part-4.ipynb

@@ -1,7 +1,7 @@
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-  "signature": "sha256:b02dd13be9c0f96660878e4759dcf7b7da0240b3dd4bd44e2891d8034d7299a9"
+  "signature": "sha256:c861c23991927808e3d10e1c2a012292dad1efcb0d56cb89e7bdb37f2770e0d4"
  },
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@@ -130,7 +130,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "Let's revisit a problem we've already solved:\n",
+      "Let's revisit a problem we've already solved in Danny's lecture on list:\n",
       "\n",
       "Pick every name from a list that begins with a vowel.\n",
       "\n",