How to get three nested enumerations in LaTeX?

Question

This is my current code. I've managed to get one next enumeration but I want a third nesting to replace me having to write 1.1.1, 1.1.2 etc.

 \begin{enumerate}
 \item Top Levek
   \begin{enumerate}
   \item Second Level
     \begin{enumerate}
     \item Third Level
     \end{enumerate}
   \end{enumerate}
 \end{enumerate}

This gives me

1 Top Level
1.1 Second Level
i Third Level

My desired output is

1 Top Level
1.1 Second Level
1.1.1 Third Level

How do I achieve this?

Also, how do I remove the indentation on the third level so it is inline with the second level?

Answer 1

You can use the enumitem package to produce:

Here's the code:

\documentclass{article}
\usepackage{enumitem}
\setlist[enumerate,1]{label=\arabic*}
\setlist[enumerate,2]{label=\theenumi.\arabic*}
\setlist[enumerate,3]{label=\theenumii.\arabic*}
\begin{document}

\begin{enumerate}
 \item Top Levek
   \begin{enumerate}
   \item Second Level
     \begin{enumerate}
     \item Third Level
     \end{enumerate}
   \end{enumerate}
 \end{enumerate}

\end{document}

The important bits are the lines

\usepackage{enumitem}
\setlist[enumerate,1]{label=\arabic*}
\setlist[enumerate,2]{label=\theenumi.\arabic*}
\setlist[enumerate,3]{label=\theenumii.\arabic*}

These specify what you want the labels to look like. I highly recommend reading the package manual if you need to tweak further. It's very to easy to read.

Edit TO get the indentation in the OP you can use:

\documentclass{article}
\usepackage{enumitem}
\setlist[enumerate]{
   leftmargin=0pt, labelindent*=0pt, labelwidth=0pt,align=left
}
\setlist[enumerate,1]{label=\arabic*}
\setlist[enumerate,2]{label=\theenumi.\arabic*}
\setlist[enumerate,3]{label=\theenumii.\arabic*}

\begin{document}

\begin{enumerate}
 \item Top Level
   \begin{enumerate}
   \item Second Level
     \begin{enumerate}
     \item Third Level
     \end{enumerate}
   \end{enumerate}
 \end{enumerate}

\end{document}

to give:

EDIT II As Mico says in the comments, for the required indentation it is easier to use \setlist[enumerate]{ wide=0pt }.

Answer 2

Is it this alignment you wish?

\documentclass{article}
\usepackage{enumitem}
\usepackage[showframe]{geometry}

\newlength{\labelwd}
\settowidth{\labelwd}{9.9.9}
\setlist[enumerate]{label*=.\arabic*, wide = 0.5em, labelwidth=\labelwd}
\setlist[enumerate, 1]{label=\arabic*}
\setlist[enumerate, 2,3]{labelindent=-\dimexpr\labelwd+\labelsep}

\begin{document}

 \begin{enumerate}[leftmargin=\dimexpr\labelwd+\labelsep + 0.5em,]
    \item Top Level. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text.
    \begin{enumerate}
        \item Second Level. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text.
        \begin{enumerate}%[labelindent = -\dimexpr1cm + \labelsep]
        \item Third Level. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text. Some more text.
        \end{enumerate}
   \end{enumerate}
\end{enumerate}

\end{document} 

Answer 3

If you don't want to use a new package, you can define new list environnement.

With my ugly solution, if you write nothing after an item and you open a new list just after, the numbers appears only one time, like show here:

LaTeX render this very well, but I do it without any care.

Here is the code:

\documentclass{article}

\newcounter{123num}
\newenvironment{123item}
  {\begin{list}{\textbf{\arabic{123num}}}
               {\usecounter{123num}
                \setlength{\leftmargin}{1.4em}
               }}
  {\end{list}}

\newcounter{sous123num}
\newenvironment{sous123item}
  {\begin{list}{\textbf{\arabic{123num}.\arabic{sous123num}}}
               {\usecounter{sous123num}
                \setlength{\labelwidth}{1.8em}
                \setlength{\leftmargin}{0.9em}
               }}
  {\end{list}}

\newcounter{soussous123num}
\newenvironment{ss123item}
  {\begin{list}{\textbf{\arabic{123num}.\arabic{sous123num}.\arabic{soussous123num}}}
               {\usecounter{soussous123num}
                \setlength{\labelwidth}{2.7em}
                \setlength{\leftmargin}{0.9em}
               }}
  {\end{list}}

\begin{document}

\begin{123item}
 \item Top Level
   \begin{sous123item}
   \item 
     \begin{ss123item}
     \item Third Level
     \end{ss123item}
   \item Second Level
   \end{sous123item}
 \end{123item}

\end{document}