One for the Books

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A book association in Belgium beat the world record for book domino chains with one that used almost 5,000 volumes and took six minutes from beginning to end (video): http://www.youtube.com/watch?v=SvrNgmwMvQY
   What is it with northern Europe and domino chains?(!) A mathematician in The Netherlands figured out how much bigger than the one before it a domino (and, presumably, a book) can be to still be toppled: http://www.technologyreview.com/view/509641/the-curious-mathematics-of-domino-chain-reactions/