''Pratchett uses his other world to hold up a distorting mirror to our own . . . he is a satirist of enormous talent'' The Times The Discworld is very much like our own - if our own were to consist of a flat planet balanced on the back of four elephants which stand on the back of a giant turtle, that is . . . ___________________''Destiny is important, see, but people go wrong when they think it controls them. It''s the other way around.'' Three witches - Granny Weatherwax, Nanny Ogg and Magrat Garlick - have gathered on a lonely heath. A king has been cruelly murdered, his throne usurped by his ambitious cousin. An infant heir and the crown of the kingdom, both missing . . . Witches don''t have these kind of dynastic problems themselves ¿ in fact, they don¿t have leaders. Granny Weatherwax was the most highly-regarded of the leaders the witches don''t have. But even she