Do not use `mathescape` in C++ code.

header.txt

@@ -74,7 +74,7 @@
   keywordstyle=\bfseries,
   language=C++,
   literate={\\f}{}0,
-  mathescape=true,
+  mathescape=false,
   morekeywords={\\brief,\\return,\\param, Dune, Eigen, MatrixXd, VectorXd, assert, Zero},
   numbers=left,
   numberstyle=\color{gray},