Formal logic presupposes a formal language. A rudimentary formal language was given by G. Boole. A formal language which was sufficient for the purpose of mathematics was constructed by Gottlob Frege in his book " Begriffsschrift, eine der arithmetischen nachgebildete Formel sprache des reinen Denkens" (1879). Since that time we have an abun dant spectrum of logics based on formal languages. There are applications mainly in mathematics ("metamathematics"), but also e. g. in philos ophy, linguistics and computer science. The most important formal language is the first order predicate calculus....