reflects all this, as the wizards must ensure that The Origin of Species is written to maintain Earth's history. At the 2006 Discworld Convention, Cohen and Stewart explained that they originally drafted a very different outline for Science of Discworld III, in which the wizards visited various different fictional versions of Mars (Ray Bradbury's Mars, H.G. Wells' Mars, Edgar Rice Burroughs' Mars, etc.), culminating in the discovery of a Discworld version of Barsoom, (a square, red world, on the back of four , on the back of a giant ). This was abandoned when it was realised both that this discovery would have to have repercussions in later books, especially if, as planned, the "Martians" invaded; and also that Barsoom was close enough to sword and sorcery in any case that transplanting it to the Discworld setting did not alter it enough to be funny. References External links Books by Ian Stewart (mathematician) 2005 books Discworld books Ebury Publishing books