In the February 1970 Word Ways, Walter Penney's cryptographic Puzzle 1 asked the reader to determine the order of a set of cards bearing letters after a single shuffle, if the original order and the new order resulting from two identical shuffles were given. The solution, with its reference to trial-and-error, was rather unsatisfactory. In this short note, we suggest a more systematic approach to such problems.
Lindon, J. A.
"Note on Repeated Letter-Shuffling,"
Word Ways: Vol. 4
, Article 12.
Available at: http://digitalcommons.butler.edu/wordways/vol4/iss3/12