The effect goes something like this...

The mentalist has his back turned.
1 - 12 cards with various location names on them have been laid out in a 3x4 grid.
2 - The volunteer places a small token on any card, its a totally free choice.
3 - Volunteer moves the token (up down, left or right, not diagonally) by spelling out of his starting location, one move for each letter.
4 - The mentalist instructs that several cards are removed.
5 - The mentalist now instructs the volunteer to move say 5 times. More cards are removed.
6 - The mentalist now instructs the volunteer to move say 7 times. More cards are removed.
7 - Ditto.
8 - Eventually there is just a single card remaining (the one with the volunteer's token on it) and this coincides with the mentalists prediction.

I have 2 effects based on this principle but I would like to explore the mathematics behind it and create my own.

If you know what this effect/principle is called or what book I can look in for info I would be most appreciative.

The principle was already old when Martin Gardner got a hold of it in Martin Gardner Presents. For a particularly clever version see Simon Aronson's "Move and Removes" in Simply Simon.

Thank you landmark. Yes, I know it's old but I like it. I will look into both these sources, much appreciated. It is very hard to research something when you do not know what it is called

Alas, I do not have either of the books that Landmark kindly cited. Any further help with the NAME of the maths principle would be appreciated as I can then look in older books in the public domain.

You might want to read the chapter on Topological Forces in Thomas Henry's wonderful book Hidden Numerical Forces.

Murf

Thank you Murf, I read your reply today and in the small window since then I have ascertained that I WANT this book. Cool recommendation,
cheers
Art

Murf
I am hot on the trail of the TH book and the phrase 'Topological forces', which I was not aware of, is extremely helpful when I want to discuss this topic, unlike my clumsy initial OP.
Art

I have the book Murf, many thanks, it is great, My head is buzzing with ideas,
Art

I love that book, and I find it surprising how few people seem to be familiar with it.

Murf

They say he has another one in the works.....

For $6!!! Wow, what a bargain! I didn't realize it had become difficult to find.

Slim King, who are the "they" that say another one is in the works, and where can I find out more?

Murf

@ Murf and slim King...
did anybody get further info on a sequel?
Art