Martin Gardner query
My Dad has been given a strangely-cut piece of paper folded into a square, which physically simulates a method for remembering Maxwell's Relations (something to do with thermodynamics, don't worry about it).

The problem is that he has posted it to me, and I have unfolded it in a curious fashion, but now cannot refold it - and neither of us knows how to use it anyway.

The kindly scientist who gave it to him said that it was based on an article in "Fun with Maths" by Martin Gardner. Now, while it has a very Martin Gardnerish sort of look (anybody here remember hexaflexagons?) I cannot find any references to a book of that name by Gardner.

The piece of paper is shaped like a square with the corners cut out. It is then folded into a square with four quadrants. You can refold it in various ways to show other panels in the quadrants. No, that probably doesn't make any sense if you haven't seen it.

Anyway, does this ring any bells with anybody? I'd dearly love to find the original reference, and help Dad refold and use it!