We introduce le, a simply typed calculus with environments as first class values. As well as the usual constructs of l and application, we have e\lbrack\lbrack a\rbrack\rbrack which evaluates term a in an environment e. Our environments are sets of variable-value pairs, but environments can also be computed by function application and evaluation in some other environments. The notion of environments here is a generalization of explicit substitutions and records. We show that the calculus has desirable properties such as subject reduction, confluence, conservativity over the simply typed lb-calculus and strong normalizability.
The main aim of our paper was to present three formal tools for comparing various axiomatic theories of truth. In Section 2 we aimed at showing that there are indeed many different approaches to defining a set of axioms for the notion of truth. In Section 3 we introduced three different \measures of strength" of axiomatic theories of truth, i.e. three reflexive and transitive relations (preorders) on the set of axiomatic theories of truth. We have explained the intuition behind each of them. The three relations were called (from the most fine-grained to the coarsest): Fujimoto definability, model-theoretical strength, proof-theoretical strength. Then in the last section we described how they order the truth theories introduced in Section 2. We observed that theories made equivalent by the coarser relation can be strictly ordered by the next one.
Niniejsza praca stanowi przegląd niedawnych wyników, zarówno opublikowanych, jak i jeszcze czekających na publikację, dotyczących różnych pojęć słabości i siły pojęcia prawdy, a także próbę ich systematyzacji i ukazania na tle szerszego nurtu badań. Omawiamy pojęcie granicy Tarskiego oddzielającej słabe i silne teorie prawdy. Omawiamy znane twierdzenia dotyczące niekonserwatywnych rozszerzeń podstawowej kompozycyjnej teorii prawdy oraz opisujemy pewną naturalną silną teorię prawdy, którą można scharakteryzować wieloma pozornie ze sobą niezwiązanymi układami aksjomatów. Na koniec przytaczamy inne możliwe eksplikacje pojęcia „siły” aksjomatycznych teorii prawdy.
EN
This paper is an exposition of some recent results concerning various notions of strength and weakness of the concept of truth, both published and not. We try to systematically present these notions and their relationship to the current research on truth. We discuss the concept of Tarski’s boundary between weak and strong theories of truth and we give an overview of nonconservativity results for the extensions of the basic compositional truth theory. Additionally, we present a natural strong theory of truth, which admits a number of apparently unrelated axiomatisations. Finally, we discuss other possible explications for the notion of ‘strength’ in axiomatic theories of truth.
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