small change in reduction

issues/reduction.ipynb

@@ -93,7 +93,7 @@
       "metadata": {},
       "source": [
         "```{exercise}\n",
-        "Let $P_3$ be the matrix mortality problem for $3\\times 3$ matrices.  Let $P_2$ and $P_4$ be defined similarly, for the $2\\times 2$ and $3\\times 3$ matrices.   Show that $P_2 \\leq P_3 \\leq P_4$.  This is a straightforward algebraic argument.\n",
+        "Let $P_3$ be the matrix mortality problem for $3\\times 3$ matrices.  Let $P_2$ and $P_4$ be defined similarly, for the $2\\times 2$ and $4\\times 4$ matrices.   Show that $P_2 \\leq P_3 \\leq P_4$.  This is a straightforward algebraic argument.\n",
         "\n",
         "Later we will see that $P_4 \\leq P_3$, but the argument will not be not as straightforward.\n",
         "```"