# Best practise: Using description environment for case differentiation

Is it semantically correct to use the description environment for case differentiation in a proof? Actually, it doesn‘t seem that a description fit, does it? But it looks correct to me. If it‘s not correct, what should I use instead?

\begin{proof}
We can differentiate three cases.
\begin{description}
\item[Case $x > 0$] If $x$ is positive. ...
\item[Case $x = 0$] Trivial.
\item[Case $x < 0$] If $x$ is negative, ...
\end{description}
That completes the proof for all $x \in \mathbb R$.
\end{proof}

• Please tell us more about the intended use case of this list. E.g., could ABC, DEF, etc span multiple lines and, if so, should the continuation lines be aligned with the start of the first line or with "Case"? How long could this list be: Three to five line items, 10 to 15 line items, or several pages worth of material?
– Mico
May 3 '20 at 18:40
• It‘s part of a proof. I differentiate several cases. Of course, the lines could span multiple lines, but normally the whole list will not extend to several pages (but nevertheless it may happen sometimes). The alignment should be part of what latex does for me. I‘m just looking for a canonical way to typeset the cases and I‘m asking because, semantically, it doesn’t look right to use a description unless it does look correct.
– ATW
May 3 '20 at 18:44
• I added some clarification in the code @Mico.
– ATW
May 3 '20 at 18:52

My impression -- note that there's a considerable amount of unavoidable subjectivity here -- is that a description environment is overkill for the use cases you've outlined.

I would stick with either an itemize (unnumbered) list environment, e.g.,

\begin{proof}
Three separate cases must be examined.
\begin{itemize}
\item Case $x > 0$: ABC
\item Case $x = 0$: DEF
\item Case $x < 0$: GHI
\end{itemize}
That completes the proof for all $x\in\mathbb{R}$.
\end{proof}


or, if the items lend themselves in a natural way to enumeration, an enumerate (numbered) list environment, e.g.,

\begin{enumerate}
\item Case $x > 0$: ABC
\item Case $x = 0$: DEF
\item Case $x < 0$: GHI
\end{enumerate}


It's reasonably straightforward to customize the appearance of such lists with the help of the enumitem package. Any such customization is probably not urgent, though. I would stick with the default, make sure that the contents of the lists are alright, and get back to customizing the appearance of list much later -- if at all.

I think it is possible, but I would not use the default boldface, so I would code it this way (thanks to @Mico for adding \mdseries):

\usepackage{enumitem}

.............
\begin{proof}
We can differentiate three cases.
\begin{description}[font=\mdseries\itshape]
\item[Case $x > 0$] If $x$ is positive. ...
\item[Case $x = 0$] Trivial.
\item[Case $x < 0$] If $x$ is negative, ...
\end{description}
That completes the proof for all $x \in \mathbb R$.
\end{proof}

• Then the case descriptions are bold and slanted (instead of being italic) which doesn‘t look right to me...
– ATW
May 3 '20 at 19:30
• @Thomas - Just change [font=\itshape] to [font=\mdseries\itshape] in order to get non-bold italics.
– Mico
May 3 '20 at 19:57
• @Mico: You're right, I should have checked. I thought it overwrote the default. May 3 '20 at 20:23
• But then the font is still not italic but slanted. There doesn't seem to be a real italic typeface for the non-serif font...mh. Why wouldn't you use the boldface?
– ATW
May 4 '20 at 16:03
• Yes italic sans fonts are rather slanted fonts. How comes you have a sans font for description items? May 4 '20 at 16:05