Rotated underbrace and overbrace in an exponential tower

Question

I would like to typeset a tower of exponentials and have underbrace and overbrace at an angle, with rotated text (e.g., "r" and "k" here). There are related questions, but none (I could see) had the underbraces at an angle.

Answer 1

\documentclass{article}
\usepackage{stackengine,graphicx,amsmath}
\def\rdots{\rotatebox[origin=l]{29}{$\scriptscriptstyle\ldots\mathstrut$}}
\begin{document}
\stackinset{r}{-2.5pt}{b}{-6pt}{\tiny\rotatebox{29}{$\underbrace{\kern25pt}_k$}}{%
\stackinset{r}{4pt}{t}{-9.0pt}{\tiny\rotatebox{29}{$\overbrace{\kern15pt}^r$}}{%
  $a^{b^{c^{d^{\rdots^n}}}}$}}
\end{document}