Changing the numbering of lemmas and theorems in the appendix

Question

I wanted to change the name of the appendix. So, I wanted my appendix name would be not Appendix A, as usual, but Appendix I.

So I use

\begin{appendix}

\renewcommand{\theequation}{I.\arabic{equation}}

% redefine the command that creates the equation no.
\setcounter{equation}{0}  % reset counter

\section*{\textbf{Appendix I}}  % use *-form to suppress numbering

....................%some text
\end{appendix}

These commands helped me to change the formulas numbering. I've tried the same 'trick' to change lemma and theorem numbering (I wanted, for example Lemma I.1, Theorem I.2) but it did not work.

Help me please with these commands.

Answer 1

You should try to change the counter of the appendix to Roman instead of changing it for every macro using it.

So try

\renewcommand{\thesection}{\Roman{section}}

instead of the equation command. (you might use the chapter counter instead, depending on your document class)

Edit: To make it clearer: instead of

\renewcommand{\theequation}{I.\arabic{equation}}
\setcounter{equation}{0}  % reset counter
\section*{\textbf{Appendix I}}  % use *-form to suppress numbering

I would try

\renewcommand{\thesection}{\Roman{section}}
\section{Appendix}

I use the automatic numbering, so the equation counter is handled automatically and the counters of Lemma, Theorem and the lot should as well.