title: How to redifine (via ENVIRON package) the "pmatrix" environment?
body: <p>I want to redefine the "pmatrix" environment provided by AMSMATH package (and changed by MATHTOOLS package) for adding good-looking delims. The code is below:</p>
  
  <pre><code>\documentclass{article}
  \usepackage{amsmath,amstools,environ}
  \RenewEnviron{pmatrix}{\PARENS{\begin{matrix}\BODY\end{matrix}}}
  </code></pre>
  
  <p>"PARENS" command is provided by MTPRO2 package to get curved left/right parensis. But it not work. Further, there's a star-ed version pmathix* envrionment (with a optional arg l/c/r), I don't have any idea either. The code I can give is below:</p>
  
  <pre><code>\documentclass{article}
  \usepackage{amsmath,amstools,environ}
  \RenewEnviron{pmatrix*}[1][c]{\PARENS{\begin{matrix*}[c]\BODY\end{matrix*}}}
  </code></pre>
  
  <p>I mail to ENVIRON package's author Will Robertson (wspr81[at]gmail[dot]com) but no reply. He maybe been seen here usually. So I logged in and posted.</p>