Representing negation in a planner system

A program is described which carries on a dialogue with the operator, accepting English statements and questions, noting the statements and answering the questions. A method is described for representing negative information. The program goes beyond previous question-answering systems in that new information can be given in English even where this entails selectively removing older information. Universal and existential 'quantifiers* and negation may be used in both statements and questions. The treatment of the quantifiers is outlined. The program uses POPLER 1.5, a PLANNER-like system.