Tabbed enumerate that is aligned with previous line

Question

I would like to be able to replicate the following image. I am not sure how to force the enumerate to align after $M_2 =$. Could anyone provide an example replicating this?

Answer 1

One option using enumitem:

\documentclass{article}
\usepackage{enumitem}

\newlength\Separation
\begin{document}

\noindent
$M_2={}$ ``On input string
\settowidth\Separation{$M_2={}$ }
\begin{enumerate}[
  nolistsep,
  label=\textbf{\arabic*.},
  leftmargin=\dimexpr\labelwidth-\labelsep+\Separation\relax
]
\item First.
\item Third.
\item Second.''
\end{enumerate}

\end{document}

The calculation for the horizontal distance for the labels is made with \labelwidth-\labelsep+\Separation, where \Separation is the width of the string you need as alignment point; $M_2={}$, in this case.

Answer 2

This can be done with a tabular:

\documentclass{article}
\usepackage{array,enumitem}
\newcolumntype{L}{>{\raggedright\arraybackslash}p{\dimexpr0.9\textwidth-2\tabcolsep\relax}}
\begin{document}
  \noindent
  \begin{tabular}{>{\centering\arraybackslash}p{0.1\textwidth}@{}L}
  $M_{2} ={}$ & ``On input string $w$:
                \begin{enumerate}[leftmargin=*,label=\textbf{\arabic*.},itemsep=0pt,before=\vspace{-0.5\baselineskip},parsep=0pt]
                \item Sweep left to right
                \item If in stage 1, 
                \item If in stage 1, the tape contained more than single 0 and the number of 0s was odd \emph{reject}''
                \end{enumerate}
  \end{tabular}
\end{document}