# Kruskal's Count - and Catching Kangaroos

Online Kruskal's Count Card Trick
The Kruskal Count was discovered by Martin Kruskal, a mathematician and physicist.

Martin Gardner popularized it with Magic Tricks. He demonstrated it with a long paragraph and used the length of the words for the step size.

Mathematically it is related to Coupling Models for Markov Chains (see Lagarias and Vandervei article below)

John Pollard uses it in Cryptography for finding the Discrete Logorithm and breaking encryption codes. Instead of a deck of cards he uses a Cyclic Group. Instead of counting the number of the card he uses a Hash Function for the step size. He called his Algorithm "The Lambda Method for Catching Kangaroos".

### To Do the Trick - 2 versions

 Using a book Using Cards ..... The Kruskal Count was discovered by Martin Kruskal, a mathematician and physicist. Martin Gardner popularized it with Magic Tricks. He demonstrated it with a long paragraph and used the length of the words for the step size. Mathematically it is related to Coupling Models for Markov Chains (see Lagarias and Vandervei article below) John Pollard uses it in Cryptography for finding the Discrete Logorithm and breaking encryption codes. Instead of a deck of cards he uses a Cyclic Group. Instead of counting the number of the card he uses a Hash Function for the step size. He called his Algorithm "The Lambda Method for Catching Kangaroos".

David Copperfield's Extremely Simple Version
James Grime Version
Explanation by James Grime