The 100 prisoners problem was first considered in 2003 by Danish computer scientist Peter Bro Miltersen who published it with Anna Gál in the proceedings of the 30. International Colloquium on Automata, Languages and Programming (ICALP). In their version, player A (the prison director) randomly colors strips of paper with the names of the players of team B (the prisoners) in red or blue and puts each strip into a different box. Some of the boxes may be empty (see below). Every player of team B must guess his color correctly after opening half of the boxes for their team to win. Initially, Milterson assumed that the winning probability quickly tends to zero with increasing number of players. However, Sven Skyum, a colleague of Miltersen at Aarhus University, brought his attention to the cycle-following strategy for the case of this problem where there are no empty boxes. To find this strategy was left open as an exercise in the publication. The paper was honored with the best paper award.