This category is on programming languages and documents that fully or partially support the basic principles of logic programming: declarative, relational programming based on first-order logic, via Horn clauses, where authors write databases of facts and rules (clauses), and users supply goals, which programs work to prove via resolution or backward chaining. Logic programming is used extensively in artificial intelligence, AI. The first such language was Prolog. On this page, languages are arranged in two groups and levels: 1) Top group: types or classes of languages. 2) Bottom group: specific languages, with their own directory category.