\def\sf{\purple}
\def\textsf#1{{\sf #1}}
\newcommand{\inference}[1]{$${#1}$$}
\newcommand{\NInd}[3]{\mbox{{\sf Ind}$(#1)(#2:=#3\,)$}}
\newcommand{\Ind}[4]{\mbox{{\sf Ind}$(#1)[#2](#3:=#4\,)$}}
\renewcommand{\medskip}{\\}