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Negation is a pretty common addition to datalog, along with group-by, max, min and other non-monotonic operators. It merely requires stratification. http://web

• cgag 13y ago
  This looks cool, I'll have to check this book out. For people who are interested, this is from Foundations of Databases (http://www.amazon.com/Foundations-Databases-The-Logical-Level/dp/0201537710/ref=cm_lmf_tit_11 http://www.amazon.com/Foundations-Databases-The-Logical-Leve...) and is available for free at the root url from jamii's link. edit: realized it's a referral link, it's not mine, it's because I got there through Rich Hickey's list of books that influenced clojure: http://www.amazon.com/Clojure-Bookshelf/lm/R3LG3ZBZS4GCTH http://www.amazon.com/Clojure-Bookshelf/lm/R3LG3ZBZS4GCTH