Cfrgtkky

I would like to learn what's the best way (most natural, canonical) to put in displayed form something like this

Maybe align?

An itemized list would be, in my mind, canonical. I say this because the math is all inline...things like align might be appropriate were the math displaystyle without surrounding text, but not here in this example.

documentclass[a4paper]{article}

usepackage{enumitem}

begin{document}

noindent the fibre or fibre category...

begin{itemize}[leftmargin=1.2in,labelsep=.2in]

item[bfseries objects] $X inmathcal{E}$ with $pX = I$

item[bfseries morphisms] $xrightarrow Y$ in $mathcal{E}_f$ are morphisms 

  in $f: Xrightarrow Y$ in $mathcal{E}$ for which $pf$ is the identity map 

  on $I$ in $mathcal{B}$.

end{itemize}

An object ...

end{document}

If you really wanted left-aligned labels, you can use the itemize option align=left. I also zeroed itemsep so that the inter-item vertical gap is smaller.

documentclass[a4paper]{article}

usepackage{enumitem}

begin{document}

noindent the fibre or fibre category...

begin{itemize}[leftmargin=1.2in,labelwidth=.8in,labelsep=.2in,itemsep=0pt,align=left]

item[bfseries objects] $X inmathcal{E}$ with $pX = I$

item[bfseries morphisms] $xrightarrow Y$ in $mathcal{E}_f$ are morphisms 

  in $f: Xrightarrow Y$ in $mathcal{E}$ for which $pf$ is the identity map 

  on $I$ in $mathcal{B}$.

end{itemize}

An object ...

end{document}

Assuming you have several of these descriptions, it is convenient to define a suitable environment:

documentclass[a4paper]{article}

usepackage{amsmath,amssymb}



newlength{categorywd}



newenvironment{category}

 {%

  settowidth{categorywd}{textbf{morphisms}}%

  addtolength{categorywd}{2em}%

  begin{list}{}{%

    setlength{leftmargin}{categorywd}%

    setlength{labelwidth}{categorywd}%

    setlength{labelsep}{0pt}%

    setlength{itemsep}{0pt}%

  }%

 }

 {end{list}}



newcommand{objects}{categorytype{objects}}

newcommand{morphisms}{categorytype{morphisms}}

newcommand{categorytype}[1]{%

  item[{makebox[categorywd][l]{quadtextbf{#1}}}]%

}





begin{document}



noindent

the textbf{fibre} or textbf{fibre category} $mathbb{E}_f=p^{-1}(I)$ over~$I$

is the category with

begin{category}

objects $X inmathbb{E}$ with $pX = I$.



morphisms $Xrightarrow Y$ in $mathbb{E}_f$ are morphisms 

  $fcolon Xrightarrow Y$ in $mathbb{E}$ for which $pf$ is the identity map 

  on $I$ in $mathbb{B}$.

end{category}

An object blah blah



end{document}

A tabularx environment is another solution:

documentclass[a4paper]{article}

usepackage{tabularx}



begin{document}



noindent the textbf{fibre} or textbf{fibre category}… medskip



noindentbegin{tabularx}{linewidth}{@{quad} >{bfseries}rX@{}}%

 objects & $X inmathcal{E}$ with $pX = I$ \

 morphisms & $xrightarrow Y$ in $mathcal{E}_f$ are morphisms

  in $f: Xrightarrow Y$ in $mathcal{E}$ for which $pf$ is the identity map

  on $I$ in $mathcal{B}$.

end{tabularx}

An object ...bigskip



noindentbegin{tabularx}{linewidth}{@{quad}>{bfseries}lX@{}}%

 objects & $X inmathcal{E}$ with $pX = I$ \

 morphisms & $xrightarrow Y$ in $mathcal{E}_f$ are morphisms

  in $f: Xrightarrow Y$ in $mathcal{E}$ for which $pf$ is the identity map

  on $I$ in $mathcal{B}$.

end{tabularx}



end{document}