[plt-scheme] equal? and shared structure

Robby wrote:

> The basic algorithm Kent used is union-find, but he did a bunch of
> tricks to avoid the large overhead when there is no sharing and then
> tricked up his tricks some more to get most uses of equal? fast.

Okay, now I am really intrigued. Can someone on this list who knows 
Dybvig hit him up for the details? --PR