Kruskal count

The Kruskal count[1][2] (also known as Kruskal's principle,[3][4][5][6][7] Dynkin–Kruskal count,[8] Dynkin's counting trick,[9] Dynkin's card trick,[10][11][12][13] coupling card trick[14][15][16] or shift coupling[10][11][12][13]) is a probabilistic concept originally demonstrated by the Russian mathematician Evgenii Borisovich Dynkin in the 1950s or 1960s[when?]

discussing coupling effects[14][15][9][16] and rediscovered as a card trick by the American mathematician Martin David Kruskal in the early 1970s[17][nb 1] as a side-product while working on another problem.

[18] It was published by Kruskal's friend[19] Martin Gardner[20][1] and magician Karl Fulves in 1975.

Rather the effect is based on the mathematical fact that the output of a Markov chain, under certain conditions, is typically independent of the input.

The output after three or more moves does not depend on the initially chosen number and therefore the magician can predict it.