99 research outputs found
Sequent Calculi for the Modal µ-Calculus over S5
We present two sequent calculi for the modal µ-calculus over S5 and prove their completeness by using classical methods. One sequent calculus has an analytical cut rule and could be used for a decision procedure the other uses a modified version of the induction rule.We also provide a completeness theorem for Kozen's Axiomatization over S5 without using the completeness result established byWalukiewicz for the modal µ-calculus over arbitrary model
Fragments and frame classes:Towards a uniform proof theory for modal fixed point logics
This thesis studies the proof theory of modal fixed point logics. In particular, we construct proof systems for various fragments of the modal mu-calculus, interpreted over various classes of frames. With an emphasis on uniform constructions and general results, we aim to bring the relatively underdeveloped proof theory of modal fixed point logics closer to the well-established proof theory of basic modal logic. We employ two main approaches. First, we seek to generalise existing methods for basic modal logic to accommodate fragments of the modal mu-calculus. We use this approach for obtaining Hilbert-style proof systems. Secondly, we adapt existing proof systems for the modal mu-calculus to various classes of frames. This approach yields proof systems which are non-well-founded, or cyclic.The thesis starts with an introduction and some mathematical preliminaries. In Chapter 3 we give hypersequent calculi for modal logic with the master modality, building on work by Ori Lahav. This is followed by an Intermezzo, where we present an abstract framework for cyclic proofs, in which we give sufficient conditions for establishing the bounded proof property. In Chapter 4 we generalise existing work on Hilbert-style proof systems for PDL to the level of the continuous modal mu-calculus. Chapter 5 contains a novel cyclic proof system for the alternation-free two-way modal mu-calculus. Finally, in Chapter 6, we present a cyclic proof system for Guarded Kleene Algebra with Tests and take a first step towards using it to establish the completeness of an algebraic counterpart
First-order modal logic in the necessary framework of objects
I consider the first-order modal logic which counts as valid those sentences which are true on every interpretation of the non-logical constants. Based on the assumptions that it is necessary what individuals there are and that it is necessary which propositions are necessary, Timothy Williamson has tentatively suggested an argument for the claim that this logic is determined by a possible world structure consisting of an infinite set of individuals and an infinite set of worlds. He notes that only the cardinalities of these sets matters, and that not all pairs of infinite sets determine the same logic. I use so-called two-cardinal theorems from model theory to investigate the space of logics and consequence relations determined by pairs of infinite sets, and show how to eliminate the assumption that worlds are individuals from Williamson’s argument
Automated proof search in non-classical logics : efficient matrix proof methods for modal and intuitionistic logics
In this thesis we develop efficient methods for automated proof search within
an important class of mathematical logics. The logics considered are the varying,
cumulative and constant domain versions of the first-order modal logics
K, K4, D, D4, T, S4 and S5, and first-order intuitionistic logic. The use of
these non-classical logics is commonplace within Computing Science and Artificial
Intelligence in applications in which efficient machine assisted proof search
is essential.
Traditional techniques for the design of efficient proof methods for classical
logic prove to be of limited use in this context due to their dependence on
properties of classical logic not shared by most of the logics under consideration.
One major contribution of this thesis is to reformulate and abstract some of these
classical techniques to facilitate their application to a wider class of mathematical
logics.
We begin with Bibel's Connection Calculus: a matrix proof method for classical
logic comparable in efficiency with most machine orientated proof methods
for that logic. We reformulate this method to support its decomposition into
a collection of individual techniques for improving the efficiency of proof search
within a standard cut-free sequent calculus for classical logic. Each technique
is presented as a means of alleviating a particular form of redundancy manifest
within sequent-based proof search. One important result that arises from this
anaylsis is an appreciation of the role of unification as a tool for removing certain
proof-theoretic complexities of specific sequent rules; in the case of classical
logic: the interaction of the quantifier rules.
All of the non-classical logics under consideration admit complete sequent
calculi. We anaylse the search spaces induced by these sequent proof systems
and apply the techniques identified previously to remove specific redundancies
found therein. Significantly, our proof-theoretic analysis of the role of unification
renders it useful even within the propositional fragments of modal and
intuitionistic logic
Proof-theoretic Semantics for Intuitionistic Multiplicative Linear Logic
This work is the first exploration of proof-theoretic semantics for a substructural logic. It focuses on the base-extension semantics (B-eS) for intuitionistic multiplicative linear logic (IMLL). The starting point is a review of Sandqvist’s B-eS for intuitionistic propositional logic (IPL), for which we propose an alternative treatment of conjunction that takes the form of the generalized elimination rule for the connective. The resulting semantics is shown to be sound and complete. This motivates our main contribution, a B-eS for IMLL
, in which the definitions of the logical constants all take the form of their elimination rule and for which soundness and completeness are established
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