\newcommand{\kf}{\ensuremath{k(\fs)}}
\newcommand{\kfs}[1]{\ensuremath{k_{#1}(\fs)}}
%\newcommand{\avg}[1]{\ensuremath{\left\langle {#1} \right\rangle}}
-\newcommand{\logp}[1]{\ensuremath{\log\!\!\!\left( {#1} \right)}}
+\newcommand{\logp}[1]{\ensuremath{\log\!\!\left( {#1} \right)}}
% \! is a negative thin space to get the paren closer to the log
\renewcommand{\r}{\ensuremath{r_f}}
\newcommand{\rs}[1]{\ensuremath{r_{f{#1}}}}% to avoid double-subscripting