diff --git a/08_dimensionality_reduction.ipynb b/08_dimensionality_reduction.ipynb
index 153e6ce..fc665c9 100644
--- a/08_dimensionality_reduction.ipynb
+++ b/08_dimensionality_reduction.ipynb
@@ -4,11 +4,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "**Chapter 8 – Dimensionality Reduction** (1st edition)\n",
+    "**Chapter 8 – Dimensionality Reduction**\n",
     "\n",
-    "**Chapter 8 – Unsupervised Learning** (2nd edition)\n",
-    "\n",
-    "_The upcoming second edition of the book extends this chapter to cover not only dimensionality reduction, but also clustering, density estimation and anomaly detection. This notebook contains all sample code and solutions to the exercises of both editions._"
+    "_This notebook contains all the sample code and solutions to the exercises in chapter 8._"
    ]
   },
   {
@@ -1464,14 +1462,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Clustering"
+    "# Extra Material – Clustering"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Introdution – Classification _vs_ Clustering"
+    "## Introduction – Classification _vs_ Clustering"
    ]
   },
   {
@@ -4341,7 +4339,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Note: the fact that you see only 3 regions in the right plot although there are 4 centroids is not a bug: the weight of the top-right cluster is much larger than the weight of the lower-right cluster, so the probability that any given point in this region belongs to the top right cluster is greater than the probability that it belongs to the lower-right cluster."
+    "Note: the fact that you see only 3 regions in the right plot although there are 4 centroids is not a bug. The weight of the top-right cluster is much larger than the weight of the lower-right cluster, so the probability that any given point in this region belongs to the top right cluster is greater than the probability that it belongs to the lower-right cluster."
    ]
   },
   {