253 research outputs found
On the Herbrand content of LK
We present a structural representation of the Herbrand content of LK-proofs
with cuts of complexity prenex Sigma-2/Pi-2. The representation takes the form
of a typed non-deterministic tree grammar of order 2 which generates a finite
language of first-order terms that appear in the Herbrand expansions obtained
through cut-elimination. In particular, for every Gentzen-style reduction
between LK-proofs we study the induced grammars and classify the cases in which
language equality and inclusion hold.Comment: In Proceedings CL&C 2016, arXiv:1606.0582
Expansion Trees with Cut
Herbrand's theorem is one of the most fundamental insights in logic. From the
syntactic point of view it suggests a compact representation of proofs in
classical first- and higher-order logic by recording the information which
instances have been chosen for which quantifiers, known in the literature as
expansion trees.
Such a representation is inherently analytic and hence corresponds to a
cut-free sequent calculus proof. Recently several extensions of such proof
representations to proofs with cut have been proposed. These extensions are
based on graphical formalisms similar to proof nets and are limited to prenex
formulas.
In this paper we present a new approach that directly extends expansion trees
by cuts and covers also non-prenex formulas. We describe a cut-elimination
procedure for our expansion trees with cut that is based on the natural
reduction steps. We prove that it is weakly normalizing using methods from the
epsilon-calculus
Integrating a Global Induction Mechanism into a Sequent Calculus
Most interesting proofs in mathematics contain an inductive argument which
requires an extension of the LK-calculus to formalize. The most commonly used
calculi for induction contain a separate rule or axiom which reduces the valid
proof theoretic properties of the calculus. To the best of our knowledge, there
are no such calculi which allow cut-elimination to a normal form with the
subformula property, i.e. every formula occurring in the proof is a subformula
of the end sequent. Proof schemata are a variant of LK-proofs able to simulate
induction by linking proofs together. There exists a schematic normal form
which has comparable proof theoretic behaviour to normal forms with the
subformula property. However, a calculus for the construction of proof schemata
does not exist. In this paper, we introduce a calculus for proof schemata and
prove soundness and completeness with respect to a fragment of the inductive
arguments formalizable in Peano arithmetic.Comment: 16 page
Proving Correctness and Completeness of Normal Programs - a Declarative Approach
We advocate a declarative approach to proving properties of logic programs.
Total correctness can be separated into correctness, completeness and clean
termination; the latter includes non-floundering. Only clean termination
depends on the operational semantics, in particular on the selection rule. We
show how to deal with correctness and completeness in a declarative way,
treating programs only from the logical point of view. Specifications used in
this approach are interpretations (or theories). We point out that
specifications for correctness may differ from those for completeness, as
usually there are answers which are neither considered erroneous nor required
to be computed.
We present proof methods for correctness and completeness for definite
programs and generalize them to normal programs. For normal programs we use the
3-valued completion semantics; this is a standard semantics corresponding to
negation as finite failure. The proof methods employ solely the classical
2-valued logic. We use a 2-valued characterization of the 3-valued completion
semantics which may be of separate interest. The presented methods are compared
with an approach based on operational semantics. We also employ the ideas of
this work to generalize a known method of proving termination of normal
programs.Comment: To appear in Theory and Practice of Logic Programming (TPLP). 44
page
Automorphisms of local fields of period and nilpotent class
Suppose is a finite field extension of containing a
primitive -th root of unity. Let be the Galois group of a
maximal -extension of with the Galois group of period and nilpotent
class . In the paper we describe the ramification filtration and relate it to an explicit form of the
Demushkin relation for . The results are given in terms of Lie
algebras attached to involved groups by the classical equivalence of the
categories of -groups and Lie algebras of nilpotent class .Comment: Substantial revision, 61 page
Effectively Solving NP-SPEC Encodings by Translation to ASP
NP-SPEC is a language for specifying problems in NP in a declarative way. Despite the fact that the semantics of the language was given by referring to Datalog with circumscription, which is very close to ASP, so far the only existing implementations are by means of ECLiPSe Prolog and via Boolean satisfiability solvers. In this paper, we present translations from NP-SPEC into ASP, and provide an experimental evaluation of existing implementations and the proposed translations to ASP using various ASP solvers. The results show that translating to ASP clearly has an edge over the existing translation into SAT, which involves an intrinsic grounding process. We also argue that it might be useful to incorporate certain language constructs of NPSPEC into mainstream ASP
Tree Grammars for the Elimination of Non-prenex Cuts
Recently a new connection between proof theory and formal language theory was introduced. It was shown that the operation of cut elimination for proofs with prenex Pi_1-cuts in classical first-order logic corresponds to computing the language of a particular type of tree grammars. The present paper extends this connection to arbitrary (i.e. non-prenex) cuts without quantifier alternations. The key to treating non-prenex cuts lies in using a new class of tree grammars, constraint grammars, which describe the relationship of the applicability of its productions by a propositional formula
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