Atomic Subformulas Research Articles

Quantum Uncertainties and Holism Seem to Render Irrelevant Qudit-Semantics.

We consider a semantics based on the peculiar holistic features of the quantum formalism. Any formula of the language gives rise to a quantum circuit that transforms the density operator associated to the formula into the density operator associated to the atomic subformulas in a reversible way. The procedure goes from the whole to the parts against the compositionality-principle and gives rise to a semantic characterization for a new form of quantum logic that has been called “Łukasiewicz quantum computational logic”. It is interesting to compare the logic based on qubit-semantics with that on qudit-semantics. Having in mind the relationships between classical logic and Łukasiewicz-many valued logics, one could expect that the former is stronger than the fragment of the latter. However, this is not the case. From an intuitive point of view, this can be explained by recalling that the former is a very weak form of logic. Many important logical arguments, which are valid either in Birkhoff and von Neumann’s quantum logic or in classical logic, are generally violated.

LOGICS FROM QUANTUM COMPUTATION WITH BOUNDED ADDITIVE OPERATORS

The theory of gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics, where the meaning of a sentence is identified with a system of qubits in a pure or, more generally, mixed state. In this framework, any formula of the language gives rise to a quantum circuit that transforms the state associated to the atomic subformulas into the state associated to the formula and vice versa. On this basis, some holistic semantic situations can be described, where the meaning of whole determines the meaning of the parts, by non-linear and anti-unitary operators. We prove that the semantics with such operators and the semantics with unitary operators turn out to characterize the same logic.

Product Łukasiewicz Quantum Logic

The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a density operator (called qumix). In this framework, any sentence α of the language gives rise to a quantum circuit that transforms the qumix associated to the atomic subformulas of α into the qumix associated to α. In this paper we enrich the language by adding a new connective which expresses truncated sum.

Almost everywhere elimination of probability quantifiers

AbstractWe obtain an almost everywhere quantifier elimination for (the noncritical fragment of) the logic with probability quantifiers, introduced by the first author in [10]. This logic has quantifiers like ∃≥3/4y which says that “for at least 3/4 of all y”. These results improve upon the 0-1 law for a fragment of this logic obtained by Knyazev [11]. Our improvements are:1. We deal with the quantifier ∃≥ry, where y is a tuple of variables.2. We remove the closedness restriction, which requires that the variables in y occur in all atomic subformulas of the quantifier scope.3. Instead of the unbiased measure where each model with universe n has the same probability, we work with any measure generated by independent atomic probabilities PR for each predicate symbol R.4. We extend the results to parametric classes of finite models (for example, the classes of bipartite graphs, undirected graphs, and oriented graphs).5. We extend the results to a natural (noncritical) fragment of the infinitary logic with probability quantifiers.6. We allow each PR, as well as each r in the probability quantifier (∃≥ry), to depend on the size of the universe.

Qubit Semantics and Quantum Trees

In the qubit semantics the meaning of any sentence α is represented by a quregister: a unit vector of the n–fold tensor product ⊗n ℂ2, where n depends on the number of occurrences of atomic sentences in α (see Cattaneo et al.). The logic characterized by this semantics, called quantum computational logic (QCL), is unsharp, because the noncontradiction principle is violated. We show that QCL does not admit any logical truth. In this framework, any sentence α gives rise to a quantum tree, consisting of a sequence of unitary operators. The quantum tree of α can be regarded as a quantum circuit that transforms the quregister associated to the occurrences of atomic subformulas of α into the quregister associated to α.

LOGICS FROM QUANTUM COMPUTATION

The theory of logical gates in quantum computation has suggested new forms of quantum logic, called quantum computational logics. The basic semantic idea is the following: the meaning of a sentence is identified with a quregister (a system of qubits) or, more generally, with a mixture of quregisters (called qumix). In this framework, any sentence α of the language gives rise to a quantum tree: a kind of quantum circuit that transforms the quregister (qumix) associated to the atomic subformulas of α into the quregister (qumix) associated to α. A variant of the quantum computational semantics is represented by the quantum holistic semantics, which permits us to represent entangled meanings. Physical models of quantum computational logics can be built by means of Mach–Zehnder interferometers.

Finding connected components of a semialgebraic set in subexponential time

Let a semialgebraic set be defined by a quantifier-free formula with atomic subformulas of the form fi>0, 0,1 ≦ i ≦ where the polynomials fiεℤ[X1,..., Xn] of degree deg (fi)<d have absolute value of the coefficients at most 2M. An algorithm is constructed which finds the connected components of the semialgebraic set (i.e., giving formulas for them) in a time that is polynomial inM (kd) ro(1). Collins' previously known method has a bound which is polynomial inM (kd) ro(1).

Random models and solvable Skolem classes

A Skolem class is a class of formulas of pure quantification theory in Skolem normal form: closed, prenex formulas with prefixes ∀…∀∃…∃. (Pure quantification theory contains quantifiers, truth-functions, and predicate letters, but neither the identity sign nor function letters.) The Gödel Class, in which the number of universal quantifiers is limited to two, was shown effectively solvable (for satisfiability) sixty years ago [G1]. Various solvable Skolem classes that extend the Gödel Class can be obtained by allowing more universal quantifiers but restricting the combinations of variables that may occur together in atomic subformulas [DG, Chapter 2]. The Gödel Class and these extensions are also finitely controllable, that is, every satisfiable formula in them has a finite model. In this paper we isolate a model-theoretic property that connects the usual solvability proofs for these classes and their finite controllability. For formulas in the solvable Skolem classes, the property is necessary and sufficient for satisfiability. The solvability proofs implicitly relied on this fact. Moreover, for any formula in Skolem normal form, the property implies the existence of a finite model.The proof of the latter implication uses the random models technique introduced in [GS] for the Gödel Class and modified and applied in [Go] to the Maslov Class. The proof thus substantiates the claim made in [Go] that random models can be adapted to the Skolem classes of [DG, Chapter 2]. As a whole, the results of this paper provide a more general, systematic approach to finite controllability than previous methods.

Complexity of deciding the first-order theory of real closed fields

Let denote an ordered field, where δi+1 is infinitesimal relative to the elements of the field ℚi 0 ≤ i < m (by definition, ℚ0=ℚ). Given a formula of the first-order theory of the real closed field ℚm, of the following form: , where P is a quantifier-free formula containing k atomic subformulas of the form (fj ≥ 0), where are polynomials such that , and the absolute value of any integer occurring in the coefficients of the polynomials fj is at most 2M. Let κ=S1+...+Sa denote the number of variables anda ⩽ n the number of quantifiers in the formula. An algorithm is constructed which decides the truth of formulas of the above form in polynomial time with respect to M, . Previously known algorithms for this problem had complexity of the order of .

Complexity of deciding Tarski algebra

Let a formula of Tarski algebra contain k atomic subformulas of the kind ( f i ⩾ 0), 1 ⩽ t ⩽ k , where the polynomials f i ∈ ℤ [ X 1 ,..., X n ] have degrees deg ( f i ) < d , let 2 M be an upper bound for the absolute value of every coeffieient of the polynomials f i , 1 ⩽ i ⩽ k , let a ⩽ n be the number of quantifier alternations in the prenex form of the formula. A decision method for Tarski algebra is described with the running time polynomial in M ( k d ) ( O ( n ) ) 4 n − 2 . Previously known decision procedures have a time complexity polynomial in ( M k d ) 2 O ( n ) .

Das Entscheidungsproblem der Klasse von Formeln, die h�chstens zwei Primformeln enthalten

For classes of formulas containing at most two atomic sub-formulas the decision problem of first-order predicate logic with identity and function variables is treated. The class of all formulas of the form Q (α ∨ β), where Q is prefix and α, β are atomic formulas or negated atomic formulas, is decidable with respect to satisfiability. The class of all formulas of the form ∀x1...∀x6(α ∨ β) is a conservative reduction class and therefore is undecidable.

Skolem reduction classes

Among the earliest and best-known theorems on the decision problem is Skolem's result [7] that the class of all closed formulas with prefixes of the form ∀···∀∃···∃ is a reduction class for satisfiability for the whole of quantification theory. This result can be refined in various ways. If the Skolem prefix alone is considered, the best result [8] is that the ∀∀∀∃ class is a reduction class, for Gödel [3], Kalmár [4], and Schütte [6] showed the ∀∀∃···∃ class to be solvable. The purpose of this paper is to describe the more complex situation that arises when (Skolem) formulas are restricted with respect to the arguments of their atomic subformulas. Before stating our theorem, we must introduce some notation.Let x, y1, y2, be distinct variables (we shall use v1, v2, ··· and w1, w2, ··· as metavariables ranging over these variables), and for each i ≥ 1 let Y(i) be the set {y1, ···, yi}. An atomic formula Pv1 ··· vk will be said to be {v1, ···, vk}-based. For any n ≥ 1, p ≥ 1, and any subsets Y1, ··· Yp of Y(n), let C(n, Y1, ···, Yp) be the class of all those closed formulas with prefix ∀y1 ··· ∀yn∃x such that each atomic subformula not containing the variable x is Yi-based for some i, 1 ≤ i ≤ p.

Linear sampling and the ∀∃∀ case of the decision problem

Let Q be the class of closed quantificational formulas ∀x∃u∀yM without identity such that M is a quantifier-free matrix containing only monadic and dyadic predicate letters and containing no atomic subformula of the form Pyx or Puy for any predicate letter P. In [DKW] Dreben, Kahr, and Wang conjectured that Q is a solvable class for satisfiability and indeed contains no formula having only infinite models. As evidence for this conjecture they noted the solvability of the subclass of Q consisting of those formulas whose atomic subformulas are of only the two forms Pxy, Pyu and the fact that each such formula that has a model has a finite model. Furthermore, it seemed likely that the techniques used to show this subclass solvable could be extended to show the solvability of the full class Q, while the syntax of Q is so restricted that it seemed impossible to express in formulas of Q any unsolvable problem known at that time.In 1966 Aanderaa refuted this conjecture. He first constructed a very complex formula in Q having an infinite model but no finite model, and then, by an extremely intricate argument, showed that Q (in fact, the subclass Q2 defined below) is unsolvable ([Aa1], [Aa2]). In this paper we develop stronger tools in order to simplify and extend the results of [Aa2]. Specifically, we show the unsolvability of an apparently new combinatorial problem, which we shall call the linear sampling problem (defined in §1.2 and §2.3). From the unsolvability of this problem there follows the unsolvability of two proper subclasses of Q, which we now define. For each i ≥ 0, let Pi be a dyadic predicate letter and let Ri be a monadic predicate letter.

The decision problem for formulas with a small number of atomic subformulas

In this paper we consider classes of quantificational formulas specified by restrictions on the number of atomic subformulas appearing in a formula. Little seems to be known about the decision problem for such classes, except that the class whose members contain at most two distinct atomic subformulas is decidable [2]. (We use “decidable” and “undecidable” throughout with respect to satisfiability rather than validity. All undecidable problems to which we refer are of maximal r.e. degree.) The principal result of this paper is the undecidability of the class of those formulas containing five atomic subformulas and with prefixes of the form ∀∃∀…∀. In fact, we show the undecidability of two sub-classes of this class: one (Theorem 1) consists of formulas whose matrices are in disjunctive normal form with two disjuncts; the other (Corollary 1) consists of formulas whose matrices are in conjunctive normal form with three conjuncts. (Theorem 1 sharpens Orevkov's result [8] that the class of formulas in disjunctive normal form with two disjuncts is undecidable.) A second corollary of Theorem 1 shows the undecidability of the class of formulas with prefixes of the form ∀…∀∃, containing six atomic subformulas, and in conjunctive normal form with three conjuncts. These restrictions to prefixes ∀∃∀…∀ and ∀…∀∃ are optimal. For by a result of the first author [5], any class of prenex formulas obtained by restricting both the number of atomic formulas and the number of universal quantifiers is reducible to a finite class of formulas, and so each such class is decidable; and the class of formulas with prefixes ∃…∃∀…∀ is, of course, decidable.