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.
appendix
environment (unless you're using some package). Use only\appendix
at the spot where appendices start; then issue the command as in the answer below. – egreg Dec 19 '12 at 11:55