An angel who can leap any distance, chased forever by a devil one square at a time
On an infinite chessboard, an 'Angel' of power k can fly up to k squares in any direction each turn, while a 'Devil' can block one square per turn, trying to eventually trap the Angel so it can never move again. John Conway asked: for some fixed power k, can the Angel always keep escaping forever, no matter how cleverly the Devil plays?
Reveal the answer
Yes — for any angel of power k of 2 or more, the Angel can always evade capture forever, guaranteeing the game never ends. The problem eluded mathematicians for over two decades after Conway popularised it in the 1990s, until several independent proofs, including by Brian Bowditch, András Máthé and Oddvar Kloster, appeared within months of each other in 2006.