Apply suggestion from @StevenClontz

Author: StevenClontz

source/linear-algebra/source/04-MX/03.ptx

@@ -230,7 +230,7 @@
             non-standard bases/coordinates as well.
         </p>
         <p>
-Let <m>\mathcal B=\setList\vec b_1,\cdots\vec b_n</m> be a basis, and consider the matrix
+Let <m>\mathcal B=\setList{\vec b_1,\cdots\vec b_n}</m> be a basis, and consider the matrix
 <m>B=\begin{bmatrix}\vec b_1&amp;\cdots&amp;\vec b_n\end{bmatrix}</m>
 <m>M_{\mathcal B}=B^{-1}</m>.
         </p>