[Tex/LaTex] Using aligned and align without amsmath

alignamsmath

I am currently working on a proceedings paper, and have realised after finishing it that only specific packages are permitted – one of which is not amsmath. As a result, many of the nice equations that I have written can now no longer be built. To save me switching back to \begin{cases} \end{cases} and giving up, I thought I would try asking on here to see if anyone could provide me with a solution?

I cannot define add any new commands before \begin{document}, so everything must be done after that point. I thought about trying to grab the relevant components from the style file, but to be perfectly honest I am not a TeX-wizard and have no idea whether this would even work.Could anyone provide me with a work-around, so that I can still use align and aligned, but by doing so after \begin{document}?

If it helps, the packages I am permitted to use are: 

\usepackage{mathptmx}       
\usepackage{helvet}         
\usepackage{courier}        
\usepackage{type1cm}        
\usepackage{graphicx}        
\usepackage[bottom]{footmisc}    
\usepackage{amssymb}    
\usepackage{amsfonts}   
\usepackage{amsbsy}   
\usepackage{amscd}   
\usepackage{amstext}   
\usepackage{dsfont}   
\usepackage[english]{babel}   
\usepackage{color}   
\usepackage{graphics}   
\usepackage{epsfig}   
\usepackage{subfigure}   
\usepackage{wrapfig}   
\usepackage{psfrag}   
\usepackage{color}   
\usepackage{url}   
\usepackage{verbatim}   
\usepackage{algorithm}   
\usepackage{algorithmic}

Edit: An MWE is as follows:

\documentclass{svmult}   
\usepackage{mathptmx}       
\usepackage{helvet}         
\usepackage{courier}        
\usepackage{type1cm}        

\usepackage{graphicx}        

\usepackage[bottom]{footmisc}

\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsbsy}
\usepackage{amscd}
\usepackage{amstext}
\usepackage{dsfont}
\usepackage[english]{babel}
\usepackage{color}
\usepackage{graphics}
\usepackage{epsfig}
\usepackage{subfigure}
\usepackage{wrapfig}
\usepackage{psfrag}
\usepackage{color}
\usepackage{url}
\usepackage{verbatim}
\usepackage{algorithm}
\usepackage{algorithmic}


\begin{document}

\begin{equation}
\label{InitSystemNL}
\left\{
\begin{aligned}
\mathcal{R} \colon= -\Delta u &= f  \quad & &\text{in} \,\, \Omega \\ u &= 0 \quad & &\text{on} \,\, \partial\Omega, \end{aligned} \right.
\end{equation}

\end{document}

Best Answer

To avoid needing to edit the existing doc you can defined a poor man's aligned as follows (but first try to get the rules changed)

enter image description here

\documentclass{article}   
\usepackage{mathptmx}       
\usepackage{helvet}         
\usepackage{courier}        
\usepackage{type1cm}        

\usepackage{graphicx}        

\usepackage[bottom]{footmisc}

\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsbsy}
\usepackage{amscd}
\usepackage{amstext}
\usepackage{dsfont}
\usepackage[english]{babel}
\usepackage{color}
\usepackage{graphics}
\usepackage{epsfig}
\usepackage{subfigure}
\usepackage{wrapfig}
\usepackage{psfrag}
\usepackage{color}
\usepackage{url}
\usepackage{verbatim}
\usepackage{algorithm}
\usepackage{algorithmic}


\begin{document}
\def\aligned{\vcenter\bgroup\let\\\cr
\halign\bgroup&\hfil${}##{}$&${}##{}$\hfil\cr}
\def\endaligned{\crcr\egroup\egroup}

\begin{equation}
\label{InitSystemNL}
\left\{
\begin{aligned}
\mathcal{R} \colon= -\Delta u &= f  \quad & &\text{in} \,\, \Omega \\ u &= 0 \quad & &\text{on} \,\, \partial\Omega, 
\end{aligned} 
\right.
\end{equation}

\end{document}
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