To get enumerated and itemized lists that have the same amounts of left-hand and right-hand indentation, I'd recommend using the enumitem
package -- which provides many extensions to and improvements over LaTeX's list environments -- and its leftmargin
and rightmargin
options. The following MWE illustrates this.
\documentclass{article}
\usepackage[margin=3cm]{geometry} % per the example in your code
\usepackage{lipsum} % for filler text
\usepackage{enumitem}
\begin{document}
\lipsum[1] % filler text
\begin{enumerate}[leftmargin=2cm,rightmargin=2cm]
\item \lipsum[2]
\end{enumerate}
\lipsum[3]
\begin{itemize}[leftmargin=1cm,rightmargin=1cm]
\item \lipsum[4]
\end{itemize}
\end{document}
Added material after receiving a comment from the OP. I'm afraid I'm not quite sure about the meaning of the question
But how do I make the indentations of the \item the same as the
original text?
The new MWE below provides four separate option settings for shaping the itemized (or, equivalently, enumerated) list items. Hopefully, one of these settings meets your needs.
\documentclass{article}
% some short filler text, ca. 3 lines long
\newcommand{\shortfiller}{Nam dui ligula, fringilla a, euismod sodales, sollicitudin vel, wisi. Morbi auctor lorem non justo. Nam lacus libero, pretium at, obortis vitae, ultricies et, tellus. Donec aliquet, tortor sed accumsan bibendum, erat ligula aliquet magna.}
\usepackage{fancyvrb}
\usepackage[margin=3cm]{geometry}
\usepackage{enumitem}
\begin{document}
\DefineShortVerb{\|}
\emph{``Normal'' text paragraph.} \shortfiller
%% Option 1
\begin{enumerate}[leftmargin=2cm, rightmargin=2cm]
\item \emph{Settings:} |[leftmargin=2cm, rightmargin=2cm]|.
\shortfiller
\end{enumerate}
\emph{``Normal'' text paragraph.} \shortfiller
%% Option 2
\begin{enumerate}[resume, wide=2cm, leftmargin=2cm, rightmargin=2cm]
\item \emph{Settings:} |[wide=2cm, leftmargin=2cm, rightmargin=2cm]|.
\shortfiller
\end{enumerate}
\emph{``Normal'' text paragraph.} \shortfiller
%% Option 3
\begin{enumerate}[resume, wide=\parindent, leftmargin=\parindent, rightmargin=\parindent]
\item \emph{Settings:} |[wide=\parindent, leftmargin=\parindent, rightmargin=\parindent]|.
\shortfiller
\end{enumerate}
\emph{``Normal'' text paragraph.} \shortfiller
%% Option 4
\begin{enumerate}[resume, wide=\parindent]
\item \emph{Setting in this and the following item:} |[wide=\parindent]|.
\shortfiller
\item \shortfiller
\end{enumerate}
\emph{``Normal'' text paragraph.} \shortfiller
\end{document}
Suppose the final setting of the list items is what you're looking for. If you want this setting to apply uniformly to all enumerated and itemized lists, you should insert the command
\setlist{wide=\parindent}
in your document's preamble, immediately after the \usepackage{enumitem}
instruction.
This requires some manual adjustment, as you have to modify the argument for widest
to be the widest number in the list. As the item numbers are right aligned, only the widest run to the margin, the rest are indented a bit.
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{enumitem}
\usepackage{showframe}
\begin{document}
\begin{enumerate}[label=(\roman*),widest=viii,itemindent=*,leftmargin=0pt]
\item Case $a\in B$
More text \setcounter{enumi}{7}
\item Case $a\in B$
more text
\end{enumerate}
\begin{enumerate}[widest=99,itemindent=*,leftmargin=0pt]
\item Case $a\in B$
More text \setcounter{enumi}{9}
\item Case $a\in B$
more text
\end{enumerate}
\end{document}
Best Answer
Use
\leftmargin=0pt
to shift the indentation to the left boundary, this works in multiply nested lists.