PolygamousRanchKid writes: A growing number of shoppers apparently need only the briefest of breaks before diving back in, especially if they can log in to shop. IBM found that online shopping jumped 16.4 percent on Christmas Day over last year, and the dollar amount of those purchases that were made using mobile devices leaped 172.9 percent. IBM tracks shopping at more than 500 websites other than Amazon.com, which is the largest. It found a huge increase in the number of shoppers making their purchases with iPhones, iPads and Android-powered mobile devices.
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"