I am trying to do a Redirect with SOME Querystring Parameters Maintained. I already know how to do a redirect with ALL parameters maintained, or with NO parameters maintained, but in this particular case, i need only ONE of them dropped.

For example, my old links for my old system were something like:

But now they are like this:

So i need to drop the "a" parameter, but keep the "id" parameter, so that i know which article to display.