Replace $math$ with \code{}.

Doc/lib/libcmath.tex

@@ -40,7 +40,7 @@ Return the hyperbolic cosine of \var{x}.
 \end{funcdesc}
 
 \begin{funcdesc}{exp}{x}
-Return the exponential value $\mbox{e}^x$.
+Return the exponential value \code{e**\var{x}}.
 \end{funcdesc}
 
 \begin{funcdesc}{log}{x}

Doc/libcmath.tex

@@ -40,7 +40,7 @@ Return the hyperbolic cosine of \var{x}.
 \end{funcdesc}
 
 \begin{funcdesc}{exp}{x}
-Return the exponential value $\mbox{e}^x$.
+Return the exponential value \code{e**\var{x}}.
 \end{funcdesc}
 
 \begin{funcdesc}{log}{x}