Frontiers of Combining Systems : Third International Workshop FroCoS 2000 Nancy France March 22 24 2000. Proceedings This book constitutes the refereed proceedings of the Third International Workshop on Frontiers of Combining Systems FroCoS 2000 held in Nancy France in March 2000.The 14 revised full papers presented together with four invited papers were carefully reviewed and selected from a total of 31 submissions. Among the topics covered are constraint processing interval narrowing rewriting systems proof planning sequent calculus type systems model checking theorem proving declarative programming logic programming and equational theories