On extremal axioms
Rudolf Carnap, Friedrich Bachmann, Herbert G. Bohnert · History and Philosophy of Logic · 1981
In the paper translated here, Carnap and Bachmann shows that the apparently metalinguistic ‘extremal' axioms that are added to some axiom systems to the effect that the foregoing axioms are to apply as broadly, or as narrowly, as possible may be formulated directly as proper axioms. They analyze such axioms into four fundamental types, with the help of a concept of ‘complete’ isomorphism.