3

For an enumerate environment with labels modified as shown, using the enumitem package, how does one combine the various other options (labelindent, leftmargin, etc.) of enumerate so that:

  • the start of each entire label "Case (a)" or "Case{b}" is indented by the amount of a normal paragraph indent; and
  • the body of each item is flush with the left margin?

The colored markup of the output from the example below should indicate graphically what I want.

[A similar question — and presumably essentially the same method would work — for when the enumerate environment uses lower-case Roman numerals, by means of option label= \upshape(\roman*).]

\documentclass[12pt]{memoir}
\usepackage{amsthm}
\usepackage{enumitem}
\usepackage{lipsum}

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
Very important!
\end{theorem}

\begin{proof}

To begin we consider all the possibilities of what may happen and what may not actually happen at all.

We now distinguish two cases.

\begin{enumerate}[label=\emph{Case (\alph*):}]

\item $a = b$.
%
Now we see that\dots\lipsum[1]

\item $a \neq b$. In this case \dots \qedhere

\end{enumerate}

\end{proof}

After establishing that result, to which we shall refer later, we now return to the previous thread of ideas.

\end{document}

Need to adjust label indent and item body left margin

3

Use the wide option for enumerate, and set itemsep and topsep to 0pt:

\documentclass[12pt]{memoir}
\usepackage{amsthm}
\usepackage{enumitem}
\usepackage{lipsum}

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
  Very important!
\end{theorem}

\begin{proof}

  To begin we consider all the possibilities of what may happen and what may not actually happen at all.

  We now distinguish two cases.

  \begin{enumerate}[label=\emph{Case (\alph*):},wide, itemsep =0pt, topsep=0pt]
    \item $a = b$.
          %
          Now we see that ... \lipsum[1]

    \item $a ≠ b$. In this case ... \qedhere

  \end{enumerate}

\end{proof}

After establishing that result, to which we shall refer later, we now return to the previous thread of ideas.

\end{document} 

enter image description here

  • While the answer by @Werner works perfectly, I prefer this one instead, because I am more easily able to modify it for the situation of using a description environment (e.g., with labels of "Necessity" and "Sufficiency") instead of an enumerate environment. – murray Nov 26 '16 at 1:39
2

It almost seems more convenient in this case to define something like a theoremcases environment that just sets the Case (.): title at the start of a paragraph every time you call \item (or, say, \caseitem):

enter image description here

\documentclass{memoir}

\usepackage{amsthm}
\usepackage{lipsum}

\newtheorem{theorem}{Theorem}

\newcounter{theoremcases}[theorem]
\renewcommand{\thetheoremcases}{\alph{theoremcases}}
\newcommand{\caseitem}{%
  \par\refstepcounter{theoremcases}%
  \textit{Case~(\thetheoremcases): }%
  \ignorespaces
}
\newenvironment{theoremcases}
  {\let\item\caseitem}
  {}

\begin{document}

\begin{theorem}
Very important!
\end{theorem}

\begin{proof}
To begin we consider all the possibilities of what may happen and what may not actually happen at all.

We now distinguish two cases.

\begin{theoremcases}
  \item $a = b$.
  %
  Now we see that\dots\lipsum[1]

  \item $a \neq b$. In this case \dots \qedhere
\end{theoremcases}
\end{proof}

After establishing that result, to which we shall refer later, we now return to the previous thread of ideas.

\end{document}

The theoremcases environment just makes \item equivalent to \caseitem, for convenience. You can also \label-and-\ref the cases, just like you would using enumitem.

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