On a Subset of all the Permutations of n Marks.

Yaakov L. Varol On a Subset of all the Permutations of n Marks. 344-346 1980 23 Comput. J. 4 db/journals/cj/cj23.html#Varol80 http://dx.doi.org/10.1093/comjnl/23.4.344