Added infinity sign back into chapter title.

IPython 2.4 was barfing on it for some unknown reason. 3.0 to the rescue.

15_HInfinity_Filters.ipynb

@@ -11,7 +11,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# H Infinity filter"
+    "# $H_\\infty$ filter"
    ]
   },
   {
@@ -261,7 +261,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "I am still mulling over how to write this chapter. In the meantime, Dan Simon has an accessible introduction here:\n",
+    "I am still mulling over how to write this chapter. In the meantime, Professor Dan Simon at Clevant State University has an accessible introduction here:\n",
     "\n",
     "http://academic.csuohio.edu/simond/courses/eec641/hinfinity.pdf\n",
     "\n",