Is appending superscripts possible?

Question

Let's say I want to write N^{eT}, but have N^e as a predefined command \Ne. Thus, I want to append the character T to the superscript of \Ne. Is this possible?

(Note that I don't want to write {\Ne}^T, since that will result in the T being one level above the e. This was adressed in Trick LaTeX into doing double superscripts by the way)

Answer 1

Or what about an empty optional argument?

\newcommand*\Ne[1][]{N^{e#1}}

Which you can use

$\Ne$ or $\Ne[T]$

Answer 2

Here is a "clever hack" inspired by (read: shamelessly copied from) the definition of math prime:

\documentclass{article}

\makeatletter
\def\Ne{N^\bgroup\e@s}
\def\e@s{%
  e\futurelet\@let@token\e@@s}
\def\e@@s{%
  \ifx^\@let@token
     \expandafter\expandafter\expandafter\e@@@s
  \else
     \egroup
  \fi}
\def\e@@@s#1#2{#2\egroup}
\makeatother

\begin{document}
\[
\Ne^T \Ne^T_5
\]
\end{document}

You can do \Ne^{}_{} but not \Ne_{}^{}, otherwise the positioning is exactly as N^{}_{}

Answer 3

I would define \Ne in the following way:

\newcommand{\Ne}{\ensuremath{N^e\vphantom{N}}}

This ensures that any following superscripts start at the same height as regular superscripts to N, but also trick TeX in thinking that it's not doubling a superscript:

\documentclass{article}
\newcommand{\Ne}{\ensuremath{N^e\vphantom{N}}}
\begin{document}
\Ne\ $\Ne^T$\ $N^{eT}$
\end{document}

Note that this will not work properly for subscripts, since the placement will be off. It would require more effort to make that work.