arXiv subjects

Guilherme V. Toledo

Publications and source records attributed to Guilherme V. Toledo.

10 recordsLinked to original sources

arXiv2026

Two generalizations of shininess

Shininess is one of the main theory combination methods in Satisfiability Modulo Theories. We present two infinite families of generalizations of it: one involving a property between gentleness and shininess, which helps us see gentleness itself as a variation of shininess; and another having no further computability requirements on the weaker theory, in addition dropping the need for smoothness. We prove these methods sharp, and compare them with existing methods.

cs.LO↗

arXiv2026

Bringing closure to theory combination properties

We consider the closure of three classical combination properties, namely, stable infiniteness, gentleness and shininess (or, equivalently for decidable theories, strong politeness), under intersection and combinability. We compute every possible intersection, and then compute the maximal set of theories that can be combined with each resulting intersection. We iterate this process until no new sets are identified. How many properties will we end up with?

cs.LO↗

arXiv2025

Characterizing Sets of Theories That Can Be Disjointly Combined

We study properties that allow first-order theories to be disjointly combined, including stable infiniteness, shininess, strong politeness, and gentleness. Specifically, we describe a Galois connection between sets of decidable theories, which picks out the largest set of decidable theories that can be combined with a given set of decidable theories. Using this, we exactly characterize the sets of decidable theories that can be combined with those satisfying well-known theory combination properties. This strengthens previous results and answers in the negative several long-standing open questions about the possibility of improving existing theory combination methods to apply to larger sets of theories. Additionally, the Galois connection gives rise to a complete lattice of theory combination properties, which allows one to generate new theory combination methods by taking meets and joins of elements of this lattice. We provide examples of this process, introducing new combination theorems. We situate both new and old combination methods within this lattice.

cs.LO↗

arXiv2025

Shininess, strong politeness, and unicorns

Shininess and strong politeness are properties related to theory combination procedures. In a paper titled "Many-sorted equivalence of shiny and strongly polite theories", Casal and Rasga proved that for decidable theories, these properties are equivalent. We refine their result by showing that: (i) shiny theories are always decidable, and therefore strongly polite; and (ii) there are (undecidable) strongly polite theories that are not shiny. This line of research is tightly related to a recent series of papers that have sought to classify all the relations between theory combination properties. We finally complete this project, resolving all of the remaining problems that were previously left open.

cs.LO↗

arXiv2025

Number theory combination: natural density and SMT

The study of theory combination in Satisfiability Modulo Theories (SMT) involves various model theoretic properties (e.g., stable infiniteness, smoothness, etc.). We show that such properties can be partly captured by the natural density of the spectrum of the studied theories, which is the set of sizes of their finite models. This enriches the toolbox of the theory combination researcher, by providing new tools to determine the possibility of combining theories. It also reveals interesting and surprising connections between theory combination and number theory.

cs.LO↗

arXiv2025

Being polite is not enough (and other limits of theory combination)

In the Nelson-Oppen combination method for satisfiability modulo theories, the combined theories must be stably infinite; in gentle combination, one theory has to be gentle, and the other has to satisfy a similar yet weaker property; in shiny combination, only one has to be shiny (smooth, with a computable minimal model function and the finite model property); and for polite combination, only one has to be strongly polite (smooth and strongly finitely witnessable). For each combination method, we prove that if any of its assumptions are removed, then there is no general method to combine an arbitrary pair of theories satisfying the remaining assumptions. We also prove new theory combination results that weaken the assumptions of gentle and shiny combination.

cs.LO↗

arXiv2022

A Category of Ordered Algebras Equivalent to the Category of Multialgebras

It is well known that there is a correspondence between sets and complete, atomic Boolean algebras (CABA's) taking a set to its power-set and, reciprocally, a complete, atomic Boolean algebra to its set of atomic elements. Of course, such a correspondence induces an equivalence between the opposite category of $\textbf{Set}$ and the category of CABA's. We extend this result by taking multialgebras over a signature $Σ$, specifically those whose non-deterministic operations cannot return the empty-set, to CABA's with their zero element removed and a structure of $Σ$-algebra compatible with its order; reciprocally, one of these "almost Boolean" $Σ$-algebras is taken to its set of atomic elements equipped with a structure of multialgebra over $Σ$. This leads to an equivalence between the category of $Σ$-multialgebras and a category of ordered $Σ$-algebras. The intuition, here, is that if one wishes to do so, non-determinism may be replaced by a sufficiently rich ordering of the underlying structures.

math.CT↗

arXiv2021

Restricted swap structures for da Costa's $C_n$ and their category

In a previous article we introduced the concept of restricted Nmatrices (in short, RNmatrices), which generalize Nmatrices in the following sense: a RNmatrix is a Nmatrix together with a {\em subset} of valuations over it, from which the consequence relation is defined. Within this semantical framework we have characterized each paraconsistent logic $C_{n}$ in the hierarchy of da Costa by means of a $(n+2)$-valued RNmatrix, which also provides a relatively simple decision procedure for each calculus (recalling that $C_1$ cannot be characterized by a single finite Nmatrix). In this paper we extend such RNmatrices for $C_{n}$ by means of what we call {\em restricted swap-structures} over arbitrary Boolean algebras, obtaining so a class of non-deterministic semantical structures which characterizes da Costa's systems. We give a brief algebraic and combinatorial description of the elements of the underlying RNmatrices. Finally, by presenting a notion of category of RNmatrices, we show that the category of RNmatrices for $C_{n}$ is in fact isomorphic to the category of non-trivial Boolean algebras.

math.LO↗

arXiv2021

Absolutely Free Hyperalgebras

It is well known from universal algebra that, for every signature $Σ$, there exist algebras over $Σ$ which are absolutely free, meaning that they do not satisfy any identities or, alternatively, satisfy the universal mapping property for the class of $Σ$-algebras. Furthermore, once we fix a cardinality of the generating set, they are, up to isomorphisms, unique, and equal to algebras of terms (or propositional formulas, in the context of logic). Equivalently, the forgetful functor, from the category of $Σ$-algebras to $\textbf{Set}$, has a left adjoint. This result does not extend to multialgebras. Not only multialgebras satisfying the universal mapping property do not exist, but the forgetful functor $\mathcal{U}$, from the category of $Σ$-multialgebras to $\textbf{Set}$, does not have a left adjoint. In this paper we generalize, in a natural way, algebras of terms to multialgebras of terms, whose family of submultialgebras enjoys many properties of the former. One example is that, to every pair consisting of a function, from a multialgebra of terms to another multialgebra, and a collection of choices (which selects how a homomorphism approaches indeterminacies), it corresponds a unique homomorphism, which ressembles the universal mapping property. Another example is that the multialgebras of terms are generated by a set that may be viewed as a strong basis, which we call the ground of the multialgebra. Submultialgebras of multialgebras of terms are what we call weakly free multialgebras. Finally, with these definitions at hand, we offer a simple proof that multialgebras with the universal mapping property for the class of all multialgebras do not exist and that $\mathcal{U}$ does not have a left adjoint.

math.LO↗

arXiv2021

A simple decision procedure for da Costa's Cn logics by Restricted Nmatrix semantics

Despite being fairly powerful, finite non-deterministic matrices are unable to characterize some logics of formal inconsistency, such as those found between $\textbf{mbCcl}$ and $\textbf{Cila}$. In order to overcome this limitation, we propose here restricted non-deterministic matrices (in short, RNmatrices), which are non-deterministic algebras together with a subset of the set of valuations. This allows us to characterize not only $\textbf{mbCcl}$ and $\textbf{Cila}$ (which is equivalent, up to language, to da Costa's logic $C_1$) but the whole hierarchy of da Costa's calculi $C_n$. This produces a novel decision procedure for these logics. Moreover, we show that the RNmatrix semantics proposed here induces naturally a labelled tableau system for each $C_n$, which constitutes another decision procedure for these logics. This new semantics allows us to conceive da Costa's hierarchy of $C$-systems as a family of (non deterministically) $(n+2)$-valued logics, where $n$ is the number of "inconsistently true" truth-values and 2 is the number of "classical" or "consistent" truth-values, for every $C_n$.

math.LO↗