Right aligned first column in a cases environment

Question

Is there a simple way to obtain a right aligned first column in the cases environment. As far as I can see, mathtools does not add such an option.

(This question might be read as a request for enhancement on mathtools... :) )

Answer 1

The mathtools package actually provides this extension as a feature already! Cases can be created using the following syntax:

\newcases{<case name>}{<space>}{%
  <left col align>}{<right col align>}{<left delim>}{<right delim>}

The regular dcases case is defined in the following way:

\newcases{dcases}{\quad}{%
  $\m@th\displaystyle{##}$\hfil}{$\m@th\displaystyle{##}$\hfil}{\lbrace}{.}

Consequently, you would probably be interested in:

\makeatletter
\newcases{mycases}{\quad}{%
  \hfil$\m@th\displaystyle{##}$}{$\m@th\displaystyle{##}$\hfil}{\lbrace}{.}
\makeatother