Sub- and superscripting style (adapted from gb4e) - subperscript.sty

% -*- LaTeX -*-
\ProvidesPackage{subperscript}
%%%%%%%%%%% AUTOMATH

% this allows _ to be used in horizontal mode (from J.Frampton):
% Reimplemented to allow this feature to be turned on and off.
% The new version also combines sub- and superscripts properly.
% -Alexis

% Sub- and superscripting functionality from gb4e, packaged by Antonio Fortin

% \automath     Make _ and ^ work outside math mode
% \noautomath   Restore normal sub/superscript behavior

{ % Temporarily change catcodes
  \catcode`\_=\active
  \catcode`\^=\active

  \global\def\automath{%
    \catcode`\_=\active
    \catcode`\^=\active
    \def_##1{\gb@ifnextchar^{\automath@two_{##1}}{\ensuremath{\sb{##1}}}}%
    \def^##1{\gb@ifnextchar_{\automath@two^{##1}}{\ensuremath{\sp{##1}}}}}
}
\def\automath@two#1#2#3#4{\ensuremath{#1{#2}\relax #3{#4}}}
% Restore default catcodes for ^, _
\def\noautomath{\catcode`\_=8 \catcode`\^=7 }

% The original \@ifnextchar discards spaces when looking for the next
% ``character''. This variant accepts any token.
\long\def\gb@ifnextchar#1#2#3{%
  \let\reserved@d=#1%
  \def\reserved@a{#2}%
  \def\reserved@b{#3}%
  \futurelet\@let@token\@gbifnch}
\def\@gbifnch{%
    \ifx\@let@token\reserved@d
      \let\reserved@c\reserved@a
    \else
      \let\reserved@c\reserved@b
    \fi
  \reserved@c}

\noautomath % On by default, for backward compatibility

%%%%%%%%%


\def\lb#1{\@ifnextchar [{\@glarph{#1}}{\@bl{#1}}}
\def\@glarph#1[#2]{\ifmmode{[}\sb{{\mathrm{#1}}\sb{#2}}\else%
                           ${[}\sb{{\mathrm{#1}}\sb{#2}}$\fi}
\def\@bl#1{\ifmmode{[}\sb{\mathrm{#1}}\;\else${[}\sb{\mathrm{#1}}\;$\fi}

\def\rb#1{\@ifnextchar [{\@grarph{#1}}{\@br{#1}}}
\def\@grarph#1[#2]{\ifmmode{]}\sb{{\mathrm{#1}}\sb{#2}}\else%
                        ${]}\sb{{\mathrm{#1}}\sb{#2}}$\fi}
\def\@br#1{\ifmmode{]}\sb{\mathrm{#1}}\;\else${]}\sb{\mathrm{#1}}\;$\fi}

%%% END_NEWSTUFF.