Question: I would like to create a numbering for a Lemma by using (i) , (ii), etc as in the yellow higlighted on the following screenshot.

[![enter image description here](https://i.stack.imgur.com/Lepys.png)](https://i.stack.imgur.com/Lepys.png)

Then, the code that I created as follows.

```
\documentclass[journal]{IEEEtran}
\newtheorem{lemma}{Lemma}

\begin{document}

\begin{lemma}\label{lemma:min_req_time}
The new sequence has following properties.
\renewcommand{\labelenumi}{\Roman{enumi}}
\begin{enumerate}
    \item The minimum required time of the robot operation is $(n-1)w + nv$ in between the processing and cleaning states, including vice versa, of every step. 
    \item In addition, the minimum required time of the robot operation is $(n+1)w + (n+2)v$ after finishing the processing or cleaning for the first time and repeating the same cycle for the next cleaning or processing.
\end{enumerate}
\end{lemma}
\end{document}

```

The result in the overleaf with Tex Live 2022 is as follows.

[![result](https://i.stack.imgur.com/0nqGj.png)](https://i.stack.imgur.com/0nqGj.png)

Can anyone suggest what needs to be amended on the code to get the numbering style of (i), (ii), etc, please?

Thank you.

Answer: 
I suggest you change

```
\renewcommand{\labelenumi}{\Roman{enumi}}

```

to

```
\renewcommand{\labelenumi}{(\roman{enumi})}

```

If you want to change the numbering style for just one `lemma` environment, execute the directive right after `\begin{lemma}`. If you want the change apply to *all* `enumerate` environment, be sure to execute the directive in the document preamble.

[![enter image description here](https://i.stack.imgur.com/CxvpX.jpg)](https://i.stack.imgur.com/CxvpX.jpg)

```
\documentclass[journal]{IEEEtran}
\newtheorem{lemma}{Lemma}
\usepackage{newtxmath} % Times Roman math font (optional)
\begin{document}

\begin{lemma}\label{lemma:min_req_time}
\renewcommand{\labelenumi}{(\roman{enumi})}
The new sequence has following properties.
\begin{enumerate}
    \item The minimum required time of the robot operation is $(n-1)w + nv$ in between the processing and cleaning states, including vice versa, of every step. 
    \item In addition, the minimum required time of the robot operation is $(n+1)w + (n+2)v$ after finishing the processing or cleaning for the first time and repeating the same cycle for the next cleaning or processing.
    \item \dots\dots
    \item \dots\dots
    \item \dots\dots
    \item \dots\dots
    \item \dots\dots
\end{enumerate}
\end{lemma}

\end{document}

```
I suggest using the `enumitem` package as it provides (in my opinion) a cleaner way of redefining the label. Furthermore it allows references to be printed in the same format. Have a look at the following example *without* `enumitem`:

```
\documentclass[journal]{IEEEtran}
\begin{document}
\renewcommand{\labelenumi}{(\roman{enumi})}
\noindent The new sequence has following properties.
\begin{enumerate}
    \item The minimum\ldots\label{item:one}
    \item In addition\ldots\label{item:two}
\end{enumerate}
Here are references to \ref{item:one} and \ref{item:two}.
\end{document}

```

This produces

[![without enumitem](https://i.stack.imgur.com/YtKX1.png)](https://i.stack.imgur.com/YtKX1.png)

If you use the above package, we can achieve the following:

```
\documentclass[journal]{IEEEtran}
\usepackage{enumitem} % <- load enumitem
\begin{document}
%\renewcommand{\labelenumi}{(\roman{enumi})} % <- not needed anymore
\noindent The new sequence has following properties.
\begin{enumerate}[label=(\roman*)] % <- specify label format
    \item The minimum\ldots\label{item:one}
    \item In addition\ldots\label{item:two}
\end{enumerate}
Here are references to \ref{item:one} and \ref{item:two}. % <- produce matching references
\end{document}

```

[![with enumitem](https://i.stack.imgur.com/eEn0p.png)](https://i.stack.imgur.com/eEn0p.png)

If you don't want the references to look like the labels, this is also no problem because you can specify `ref`: Using e.g. `\begin{enumerate}[label=(\roman*),ref=[\alph*-]` you will get labels like `(i)`, `(ii)`, but references like `[a-`, `[b-` (no idea why you should want this, but it is possible).

It is also possible to make these changes globally if you put `\setlist[enumerate]{label=(\roman*)}` in the preamble.