I also don't know under what terms it was distributed and I don't know if Vafeades is still available. I did try to contact him though, but I think he's not at Trinity anymore.
An important difference between SYMMGRP.MAX and PDELIE is (from what I know from Hereman's comparisons) that PDELIE can solve the determining equations automatically, which could be a big advantage (time saving). But being able to solve systems of pde's automatically might mean it depends on many other original macsyma functionalities so porting to maxima might be difficult.
> Date: Sat, 17 Mar 2012 12:46:01 -0600
> Subject: Re: [Maxima] pdelie from peter vafeades
> From: robert.dodier at gmail.com
> To: nijso at hotmail.com
> CC: maxima at math.utexas.edu
>
> On 3/17/12, nijso beishuizen <nijso at hotmail.com> wrote:
>
> > Does somebody know if pdelie from peter vafeades is available for maxima? It
> > used to be in macsyma in the '90's but I thought it was also in maxima.
>
> I don't know anything about pdelie, but maybe you can get in touch
> with the author to ask him if he is interested in contributing it to Maxima.
> Seems like a long shot but what the heck.
>
> I wonder under what terms pdelie was contributed to Macsyma.
> Maybe the license granted to Macsyma was relatively broad,
> so (again speculating here) perhaps it would apply to Maxima as well.
> I guess the only way to find out is to get a copy of Macsyma and
> see if there is any kind of license statement for pdelie.
>
> best
>
> Robert Dodier