Gentler intro. repeat.

DrHarveyWashingtonBanks.ipynb

@@ -890,8 +890,15 @@
    "source": [
     "When we think about how to build up our clustering equation, or model Universe, we need to ensure that anything we add has the right symmetries of the problem at hand, otherwise it's not a valide description.  Both Copernicus and Einstein believed that physics understood everyone to be equal, and our model should satisfy their viewpoint also.  By imposing symmetries on our models, we are just stipulating that the laws of the Universe should be the same in one place, or at one speed, as at any other.  \n",
     "\n",
-    "In this example, this is why our model $s^2$ but not $s$; If we were to include $s$, not all observers would agree."
+    "In this example, this is why our model includes the square of $s^2$, but not $s$; If we were to include $s$, not all observers would agree."
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {