scholarly journals On an interpretation of second order quantification in first order intuitionistic propositional logic

1992 ◽  
Vol 57 (1) ◽  
pp. 33-52 ◽  
Author(s):  
Andrew M. Pitts
Keyword(s):  
Propositional Logic ◽  
Heyting Algebra ◽  
Propositional Calculus ◽  
Interpolation Theorem ◽  
Second Order ◽  
Heyting Algebras ◽  
Intuitionistic Propositional Logic ◽  
First Order ◽  
Intuitionistic Propositional Calculus ◽  
Algebraic Counterpart

AbstractWe prove the following surprising property of Heyting's intuitionistic propositional calculus, IpC. Consider the collection of formulas, ϕ, built up from propositional variables (p, q, r, …) and falsity (⊥) using conjunction (∧), disjunction (∨) and implication (→). Write ⊢ϕ to indicate that such a formula is intuitionistically valid. We show that for each variable p and formula ϕ there exists a formula Apϕ (effectively computable from ϕ), containing only variables not equal to p which occur in ϕ, and such that for all formulas ψ not involving p, ⊢ψ → Apϕ if and only if ⊢ψ → ϕ. Consequently quantification over propositional variables can be modelled in IpC, and there is an interpretation of the second order propositional calculus, IpC2, in IpC which restricts to the identity on first order propositions.An immediate corollary is the strengthening of the usual interpolation theorem for IpC to the statement that there are least and greatest interpolant formulas for any given pair of formulas. The result also has a number of interesting consequences for the algebraic counterpart of IpC, the theory of Heyting algebras. In particular we show that a model of IpC2 can be constructed whose algebra of truth-values is equal to any given Heyting algebra.

scholarly journals The decidability of dependency in intuitionistic propositional logic

1995 ◽  
Vol 60 (2) ◽  
pp. 498-504 ◽  
Author(s):  
Dick de Jongh ◽  
L. A. Chagrova
Keyword(s):  
Propositional Logic ◽  
Infinite Sequence ◽  
Propositional Calculus ◽  
Interpolation Theorem ◽  
Intuitionistic Propositional Logic ◽  
Uniform Interpolation

AbstractA definition is given for formulae A1, …, An in some theory T which is formalized in a propositional calculus S to be (in)dependent with respect to S. It is shown that, for intuitionistic propositional logic IPC, dependency (with respect to IPC itself) is decidable. This is an almost immediate consequence of Pitts’ uniform interpolation theorem for IPC. A reasonably simple infinite sequence of IPC-formulae Fn (p, q) is given such that IPC-formulae A and B are dependent if and only if at least on of the Fn (A, B) is provable.

The metatheory of the classical propositional calculus is not axiomatizable

1985 ◽  
Vol 50 (2) ◽  
pp. 451-457 ◽  
Author(s):  
Ian Mason
Keyword(s):  
Propositional Logic ◽  
Propositional Calculus ◽  
Interpolation Property ◽  
Interpolation Theorem ◽  
Order Logic ◽  
First Order Logic ◽  
Elementary Property ◽  
Classical Propositional Logic ◽  
Open Problems ◽  
First Order

In this paper we investigate the first order metatheory of the classical propositional logic. In the first section we prove that the first order metatheory of the classical propositional logic is undecidable. Thus as a mathematical object even the simplest of logics is, from a logical standpoint, quite complex. In fact it is of the same complexity as true first order number theory.This result answers negatively a question of J. F. A. K. van Benthem (see [van Benthem and Doets 1983]) as to whether the interpolation theorem in some sense completes the metatheory of the calculus. Let us begin by motivating the question that we answer. In [van Benthem and Doets 1983] it is claimed that a folklore prejudice has it that interpolation was the final elementary property of first order logic to be discovered. Even though other properties of the propositional calculus have been discovered since Craig's orginal paper [Craig 1957] (see for example [Reznikoff 1965]) there is a lot of evidence for the fundamental nature of the property. In abstract model theory for example one finds that very few logics have the interpolation property. There are two well-known open problems in this area. These are1. Is there a logic satisfying the full compactness theorem as well as the interpolation theorem that is not equivalent to first order logic even for finite models?2. Is there a logic stronger than L(Q), the logic with the quantifierthere exist uncountably many, that is countably compact and has the interpolation property?

On second order intuitionistic propositional logic without a universal quantifier

2009 ◽  
Vol 74 (1) ◽  
pp. 157-167 ◽  
Author(s):  
Konrad Zdanowski
Keyword(s):  
Propositional Logic ◽  
Second Order ◽  
Universal Quantifier ◽  
Intuitionistic Propositional Logic ◽  
Glivenko’S Theorem ◽  
Free Variables ◽  
Universal Quantification

AbstractWe examine second order intuitionistic propositional logic, IPC2. Let ℱ∃ a be the set of formulas with no universal quantification. We prove Glivenko's theorem for formulas in ℱ∃ that is, for φ ∈ ℱ∃, φ is a classical tautology if and only if ┐┐φ is a tautology of IPC2. We show that for each sentence φ ∈ ℱ∃ (without free variables), φ is a classical tautology if and only if φ is an intuitionistic tautology. As a corollary we obtain a semantic argument that the quantifier ∀ is not definable in IPC2 from ⊥, ⋁, ⋀, →, ∃.

Predicate calculus

2018 ◽  
Author(s):  
Timothy Smiley
Keyword(s):  
Propositional Calculus ◽  
Second Order ◽  
Order Logic ◽  
Predicate Calculus ◽  
First Order Logic ◽  
Complex Predicates ◽  
Modern Logic ◽  
Form Complex ◽  
First Order ◽  
Second Order Logic

The predicate calculus is the dominant system of modern logic, having displaced the traditional Aristotelian syllogistic logic that had been the previous paradigm. Like Aristotle’s, it is a logic of quantifiers – words like ‘every’, ‘some’ and ‘no’ that are used to express that a predicate applies universally or with some other distinctive kind of generality, for example ‘everyone is mortal’, ‘someone is mortal’, ‘no one is mortal’. The weakness of syllogistic logic was its inability to represent the structure of complex predicates. Thus it could not cope with argument patterns like ‘everything Fs and Gs, so everything Fs’. Nor could it cope with relations, because a logic of relations must be able to analyse cases where a quantifier is applied to a predicate that already contains one, as in ‘someone loves everyone’. Remedying the weakness required two major innovations. One was a logic of connectives – words like ‘and’, ‘or’ and ‘if’ that form complex sentences out of simpler ones. It is often studied as a distinct system: the propositional calculus. A proposition here is a true-or-false sentence and the guiding principle of propositional calculus is truth-functionality, meaning that the truth-value (truth or falsity) of a compound proposition is uniquely determined by the truth-values of its components. Its principal connectives are negation, conjunction, disjunction and a ‘material’ (that is, truth-functional) conditional. Truth-functionality makes it possible to compute the truth-values of propositions of arbitrary complexity in terms of their basic propositional constituents, and so develop the logic of tautology and tautological consequence (logical truth and consequence in virtue of the connectives). The other invention was the quantifier-variable notation. Variables are letters used to indicate things in an unspecific way; thus ‘x is mortal’ is read as predicating of an unspecified thing x what ‘Socrates is mortal’ predicates of Socrates. The connectives can now be used to form complex predicates as well as propositions, for example ‘x is human and x is mortal’; while different variables can be used in different places to express relational predicates, for example ‘x loves y’. The quantifier goes in front of the predicate it governs, with the relevant variable repeated beside it to indicate which positions are being generalized. These radical departures from the idiom of quantification in natural languages are needed to solve the further problem of ambiguity of scope. Compare, for example, the ambiguity of ‘someone loves everyone’ with the unambiguous alternative renderings ‘there is an x such that for every y, x loves y’ and ‘for every y, there is an x such that x loves y’. The result is a pattern of formal language based on a non-logical vocabulary of names of things and primitive predicates expressing properties and relations of things. The logical constants are the truth-functional connectives and the universal and existential quantifiers, plus a stock of variables construed as ranging over things. This is ‘the’ predicate calculus. A common option is to add the identity sign as a further logical constant, producing the predicate calculus with identity. The first modern logic of quantification, Frege’s of 1879, was designed to express generalizations not only about individual things but also about properties of individuals. It would nowadays be classified as a second-order logic, to distinguish it from the first-order logic described above. Second-order logic is much richer in expressive power than first-order logic, but at a price: first-order logic can be axiomatized, second-order logic cannot.

Structures and first-order logic

2004 ◽  
Author(s):  
Shawn Hedman
Keyword(s):  
Propositional Logic ◽  
Function Symbol ◽  
Second Order ◽  
Order Logic ◽  
First Order Logic ◽  
Ternary Relation ◽  
Specific Element ◽  
First Order ◽  
Lower Case ◽  
Second Order Logic

First-order logic is a richer language than propositional logic. Its lexicon contains not only the symbols ∧, ∨, ￢, →, and ↔ (and parentheses) from propositional logic, but also the symbols ∃ and ∀ for “there exists” and “for all,” along with various symbols to represent variables, constants, functions, and relations. These symbols are grouped into five categories. • Variables. Lower case letters from the end of the alphabet (. . . x, y, z) are used to denote variables. Variables represent arbitrary elements of an underlying set. This, in fact, is what “first-order” refers to. Variables that represent sets of elements are called second-order. Second-order logic, discussed in Chapter 9, is distinguished by the inclusion of such variables. • Constants. Lower case letters from the beginning of the alphabet (a, b, c, . . .) are usually used to denote constants. A constant represents a specific element of an underlying set. • Functions. The lower case letters f, g, and h are commonly used to denote functions. The arguments may be parenthetically listed following the function symbol as f(x1, x2, . . . , xn). First-order logic has symbols for functions of any number of variables. If f is a function of one, two, or three variables, then it is called unary, binary, or ternary, respectively. In general, a function of n variables is called n-ary and n is referred to as the arity of the function. • Relations. Capital letters, especially P, Q, R, and S, are used to denote relations. As with functions, each relation has an associated arity. We have an infinite number of each of these four types of symbols at our disposal. Since there are only finitely many letters, subscripts are used to accomplish this infinitude. For example, x1, x2, x3, . . . are often used to denote variables. Of course, we can use any symbol we want in first-order logic. Ascribing the letters of the alphabet in the above manner is a convenient convention. If you turn to a random page in this book and see “R(a, x, y),” you can safely assume that R is a ternary relation, x and y are variables, and a is a constant.

Embedding first order predicate logic in fragments of intuitionistic logic

1976 ◽  
Vol 41 (4) ◽  
pp. 705-718 ◽  
Author(s):  
M. H. Löb
Keyword(s):  
Intuitionistic Logic ◽  
Predicate Logic ◽  
Propositional Calculus ◽  
Expressive Power ◽  
Predicate Calculus ◽  
First Order ◽  
Intuitionistic Propositional Calculus ◽  
Individual Variables ◽  
The One ◽  
Order Predicate Calculus

Some syntactically simple fragments of intuitionistic logic possess considerable expressive power compared with their classical counterparts.In particular, we consider in this paper intuitionistic second order propositional logic (ISPL) a formalisation of which may be obtained by adding to the intuitionistic propositional calculus quantifiers binding propositional variables together with the usual quantifier rules and the axiom scheme (Ex), where is a formula not containing x.The main purpose of this paper is to show that the classical first order predicate calculus with identity can be (isomorphically) embedded in ISPL.It turns out an immediate consequence of this that the classical first order predicate calculus with identity can also be embedded in the fragment (PLA) of the intuitionistic first order predicate calculus whose only logical symbols are → and (.) (universal quantifier) and the only nonlogical symbol (apart from individual variables and parentheses) a single monadic predicate letter.Another consequence is that the classical first order predicate calculus can be embedded in the theory of Heyting algebras.The undecidability of the formal systems under consideration evidently follows immediately from the present results.We shall indicate how the methods employed may be extended to show also that the intuitionistic first order predicate calculus with identity can be embedded in both ISPL and PLA.For the purpose of the present paper it will be convenient to use the following formalisation (S) of ISPL based on [3], rather than the one given above.

An algebraic approach to intuitionistic connectives

2001 ◽  
Vol 66 (4) ◽  
pp. 1620-1636 ◽  
Author(s):  
Xavier Caicedo ◽  
Roberto Cignoli
Keyword(s):  
Algebraic Approach ◽  
Propositional Calculus ◽  
Heyting Algebras ◽  
Classical Formula ◽  
Double Negation ◽  
Intermediate Logic ◽  
Intermediate Logics ◽  
Intuitionistic Propositional Calculus ◽  
Third Law

Abstract.It is shown that axiomatic extensions of intuitionistic propositional calculus defining univocally new connectives, including those proposed by Gabbay, are strongly complete with respect to valuations in Heyting algebras with additional operations. In all cases, the double negation of such a connective is equivalent to a formula of intuitionistic calculus. Thus, under the excluded third law it collapses to a classical formula, showing that this condition in Gabbay's definition is redundant. Moreover, such connectives can not be interpreted in all Heyting algebras, unless they are already equivalent to a formula of intuitionistic calculus. These facts relativize to connectives over intermediate logics. In particular, the intermediate logic with values in the chain of length n may be “completed” conservatively by adding a single unary connective, so that the expanded system does not allow further axiomatic extensions by new connectives.

scholarly journals Sobre a lógica deôntica não-clássica

1987 ◽  
Vol 19 (55) ◽  
pp. 19-37
Author(s):  
Leila Z. Puga ◽  
Newton C.A. Da Costa
Keyword(s):  
Propositional Logic ◽  
Ethical Theory ◽  
Classical System ◽  
Propositional Calculus ◽  
Moral Dilemmas ◽  
Prima Facie ◽  
First Order ◽  
Starting Point ◽  
Expository Paper ◽  
Classical Propositional Calculus

Our starting point, in this basically expository paper, is the study of a classical system of deontic propositional logic, classical in the sense that it constitutes an extension of the classical propositional calculus. It is noted, then, that the system excludes ab initio the possibility of the existence of real moral dilemmas (contradictory obligations and prohibitions), and also can not cope smoothly with the so-called prima facie moral dilemmas. So, we develop a non-classical, paraconsistent system of propositional deontic logic which is compatible with such dilemmas, real or prima facie. In our paraconsistent system one can handle them neatly, in particular one can directly investigate their force, operational meaning, and the most important consequences of their acceptance as not uncommon moral facts. Of course, we are conscious that other procedures for dealing with them are at hand, for example by the weakening of the specific deontic axioms. It is not argued that our procedure is the best, at least as regards the present state of the issue. We think only that owing, among other reasons, to the circumstance that the basic ethical concepts are intrinsically vague, it seems quite difficult to get rid of moral dilemmas and of moral deadlocks in general. Apparently this speaks in favour of a paraconsistent approach to ethics. At any rate, a final appraisal of the possible solutions to the problem of dilemmas and deadlocks, if there is one, constitutes a matter of ethical theory and not only of logic. On the other hand, the paraconsistency stance looks likely to be relevant also in the field of legal logic. It is shown, in outline, that the systems considered are sound and complete, relative to a natural semantics. All results of this paper can be extended to first-order and to higher-order logics. Such extensions give rise to the question of the transparency (or oppacity) of the deontic contexts. As we shall argue in forthcoming articles, they normally are transparent. [L.Z.P., N.C.A. da C.] (PDF en portugués)

Generalized interpolation theorems

1972 ◽  
Vol 37 (2) ◽  
pp. 343-351
Author(s):  
Stephen J. Garland
Keyword(s):  
Interpolation Theorem ◽  
Second Order ◽  
Cut Elimination ◽  
Real Numbers ◽  
Craig Interpolation ◽  
First Order ◽  
Order Variable ◽  
Analytic Sets ◽  
Image Position ◽  
Special Case

Chang [1], [2] has proved the following generalization of the Craig interpolation theorem [3]: For any first-order formulas φ and ψ with free first- and second-order variables among ν1, …, νn, R and ν1, …, νn, S respectively, and for any sequence Q1, …, Qn of quantifiers such that Q1 is universal whenever ν1 is a second-order variable, ifthen there is a first-order formula θ with free variables among ν1, …, νn such that(Note that the Craig interpolation theorem is the special case of Chang's theorem in which Q1, …, Qn are all universal quantifiers.) Chang also raised the question [2, Remark (k)] as to whether the Lopez-Escobar interpolation theorem [6] for the infinitary language Lω1ω possesses a similar generalization. In this paper, we show that the answer to Chang's question is affirmative and, moreover, that several interpolation theorems for applied second-order languages for number theory also possess such generalizations.Maehara and Takeuti [7] have established independently proof-theoretic interpolation theorems for first-order logic and Lω1ω which have as corollaries both Chang's theorem and its analog for Lω1ω. Our proofs are quite different from theirs and rely on model-theoretic techniques stemming from the analogy between the theory of definability in Lω1ω and the theory of Borel and analytic sets of real numbers, rather than the technique of cut-elimination.

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