The Kloster solution[0] solves it in a more direct way, by showing that for each action the devil takes the angel can take a counter action by limiting it's own

The Kloster solution[0] solves it in a more direct way, by showing that for each action the devil takes the angel can take a counter action by limiting it's own moves. In the one proof is the realization that sometimes it's easier to solve a smaller problem then prove equivalence to a harder problem, and in the other is the realization that sometimes voluntarily reducing the number of actions can lead to a simpler solution. Both are pretty good tools to have under one's belt. [0] - http://home.broadpark.no/~oddvark/angel/kloster.html http://home.broadpark.no/~oddvark/angel/kloster.html