[Tex/LaTex] clearpage with appendices

Question

I am compiling my dissertation chapters. When I wrote a chapter in a standalone Latex file, the file did compile without any error. However, when I copied the text body from the standalone to an "input" file, I get the following error message:

! Undefined control sequence.
\clear@ppage ->\if@openright
\cleardoublepage \else \clearpage \fi
l.103 \begin{appendices}
The control sequence at the end of the top line
of your error message was never \def'ed.

Here is a minimal example which reproduces this error:

%Codes in the main latex file
\documentclass[oneside,final, letterpaper]{ucr}
\usepackage{lipsum}
\usepackage[toc, page]{appendix} %Package used to create appendix

\begin{document}
\input{chapter1}
\end{document}

%Codes in the inputted file "chapter1"
\section{Intro}

\lipsum

\begin{appendices}
1. It shows error.
\end{appendices}

I will appreciate if someone could guide me here.

Answer 1

The class ucr is incompatible with the package appendix. However, the class supports the inclusion of appendices in the table of contents, with their page numbers. I'm not sure what you want the appendix package for, but you don't need it for those features, at least. Rather than the appendices environment, just use \appendix as shown in the sample appendix.tex.

\begin{filecontents}{\jobname-ch1.tex}
\chapter{Intro}

\lipsum
\appendix
\chapter{Aardvark Appendectomies 1456/1567}
\begin{enumerate}
  \item This appendix will be added to the table of contents, together with its page number.
  \item No package is necessary.
  \item No error is thrown.
\end{enumerate}

\end{filecontents}

\documentclass[oneside,final, letterpaper]{ucr}
\usepackage{lipsum}

\begin{document}
\tableofcontents
\input{\jobname-ch1}
\end{document}