Author: Damir Dzhafarov

Recursive counterexamples and the foundational standpoint

Benedict Eastaugh

Recursive counterexamples are classical mathematical theorems that are made false by restricting their quantifiers to computable objects. Historically, they have been important for analysing the mathematical limitations of foundational programs such as constructivism or predicativism. For example, the least upper bound principle is recursively false, and thus unprovable by constructivists. In this talk I will argue that while recursive counterexamples are valuable for analysing foundational positions from an external, set-theoretic point of view, the approach is limited in its applicability because the results themselves are not accessible to the foundational standpoints under consideration. This limitation can be overcome, to some extent, by internalising the recursive counterexamples within a theory acceptable to a proponent of a given foundation; this is, essentially, the method of reverse mathematics. I will examine to what extent the full import of reverse mathematical results can be appreciated from a given foundational standpoint, and propose an analysis based on an analogy with Brouwer’s weak and strong counterexamples. Finally, I will argue that, at least where the reverse mathematical analysis of foundations is concerned, the epistemic considerations above show that reverse mathematics should be carried out within a weak base theory such as RCA0, rather than by studying ω-models from a set-theoretic perspective.

De Re and De Dicto Knowledge of Mathematical Statements

Marianna Antonutti

In this talk, I will apply the de re/de dicto distinction to the analysis of mathematical statements and knowledge claims in mathematics. A proof will be said to provide de dicto knowledge of a mathematical statement if it provides knowledge of a purely existential statement, and to provide de re knowledge when it carries additional information concerning the identity criteria for the objects that are proven to exist. I will examine two case studies, one from abstract algebra and one from discrete mathematics, and I will suggest that reverse mathematics can help measuring the ‘de re content’ of two different proofs of the same theorem, and that the de re/de dicto distinction introduced here lines up with certain model theoretic properties of subsystems of second order arithmetic, such as the existence of certain kinds of minimal model. Furthermore, I will argue that there are good reasons not to identify the de re content of a proof with its constructive content nor with its predicative content.

How to model the probabilities of conditionals

Branden Fitelson

David Lewis (and others) have famously argued against Adams’s Thesis (that the probability of a conditional is the conditional probability of its consequent, given it antecedent) by proving various “triviality results.” In this paper, I argue for two theses — one negative and one positive. The negative thesis is that the “triviality results” do not support the rejection of Adams’s Thesis, because Lewisian “triviality based” arguments against Adams’s Thesis rest on an implausibly strong understanding of what it takes for some credal constraint to be a rational requirement (an understanding which Lewis himself later abandoned in other contexts). The positive thesis is that there is a simple (and plausible) way of modeling the probabilities of conditionals, which (a) obeys Adams’s Thesis, and (b) avoids all of the existing triviality results.

At-issueness in direct quotation: the case of Mayan quotatives

Scott AnderBois

In addition to verba dicendi, languages have a bunch of different other grammatical devices for encoding reported speech. While not common in Indo-European languages, two of the most common such elements cross-linguistically are reportative evidentials and quotatives. Quotatives have been much less discussed then either verba dicendi or reportatives, both in descriptive/typological literature and especially in formal semantic work. While quotatives haven’t been formally analyzed in detail previously to my knowledge, several recent works on reported speech constructions in general have suggested in passing that they pattern either with verba dicendi or with reportatives. Drawing on data from Yucatec Maya, I argue that they differ from both since they present direct quotation (like verba dicendi) but make a conventional at-issueness distinction (like reportatives). To account for these facts, I develop an account of quotatives by combining an extended Farkas & Bruce 2010-style discourse scoreboard with bicontextualism (building on Eckardt 2014’s work on Free Indirect Discourse).

An Introduction to Deep Fried Logic

Logic is Contractionless and Relevant, but Logic is (Accidentally) Contractionless and Relevant: An Introduction to Deep Fried Logic

Shay Logan

Logic, according to Beall, is the universal entailment relation. I claim that this forces us to accept that logic is contractionless and relevant. But neither relevance nor contraction-freedom, important as these features have been in the literature on logic and its philosophy, play a role in my argument. Instead, they are emergent features — logical accidents, if you will. Along the way I will familiarize us with a novel (and delicious) semantic theory that I call deep fried semantics.

How to compute with an infinite time Turing machine?

Sabrina Ouazzani

In this talk, we present infinite time Turing machines (ITTM), from the original definition of the model to some new infinite time algorithms.

We will present algorithmic techniques that allow to highlight some properties of the ITTM-computable ordinals. In particular, we will study gaps in ordinal computation times, that is to say, ordinal times at which no infinite time program halts.

Residuals and Conjugates in Positive Substructural Logics

Andrew Tedder

While the relations between an operation and its residuals play an essential role in substructural logic, a closely related relation between operations is that of conjugation — so closely related that with Boolean negation, the conjugates and residuals of an operation are interdefinable. In this talk extensions of Positive Non-Associative Lambek Calculus including conjugates (and residuals) of fusion are investigated. Some interesting properties of the conjugates are discussed, a proof system is presented, its adequacy questioned, and some further logics with conjugated operations are pondered.

Routley-Meyer relational semantics for some variants of Bradys´s 4-valued matrix

Sanda María López Velasco

On the one hand, the well-known logic BN4 was defined by R.T. Brady in 1982 and can be considered as the 4-valued logic of the relevant conditional. On the other hand, Routley-Meyer type ternary relational semantics is the semantics introduced by these authors in order to model the logic of relevance. Part of my current research involves applying a R-M semantics to different logics built upon some variants of MBN4 (the matrix of BN4) which verify the Routley and Meyer basic logic B.

The aim of this talk is to display these logics briefly and the reason why they could be of some interest. I will also explain how a R-M semantics can be applied to them.  Considering this, I will provide a general outline of the soundness and completeness theorems, valid for all these logics, and focus on the (corresponding) postulates proofs, which on the contrary need to be specified in each of these logics.

UConn Logic Group Launches New Certificate Program

The Logic Group is pleased to announce that the Graduate Certificate in Logic is now accredited—which means that we can start awarding it!

A website explaining the certificate in detail is in the works. We hope to have this up by the time the new semester starts.

In the meantime, here is a rough summary:

Any UConn graduate student can get the Graduate Certificate in Logic as an additional qualification.  There are barely any requirements in addition to what graduate student members of the Logic Group are doing already:  participate in the Logic Colloquium, 12 credits from any graduate course in logic, broadly construed, from any department, and these courses must be from at least two different departments (it’s an interdisciplinary certificate, after all).  These courses are not in addition to the courses you’re taking already for MA or PhD, but the very same courses you’re taking anyway.  You can find a list of logic course below, but other courses might qualify—just ask.

The participation in the Logic Colloquium needs to be made official by way of taking a one-credit independent study with one of the logic certificate directors (or any other Logic Group faculty member who is willing), with the Logic Colloquium as “course content”.  Please contact any of the three logic certificate directors, Magda, Damir, or Marcus, if you have any questions about any of this or to apply for a having the logic certificate awarded.

Graduate Courses in Logic (examples):

  • CSE 5102 – Advances Programming Languages
  • CSE 5506 – Computational Complexity
  • LING 5410 – Semantics I
  • LING 5420 – Semantics II
  • LING 6410 – Semantics Seminar
  • LING 6420 – Topics in Semantics
  • MATH 5026 – Topics in Mathematical Logic
  • MATH 5260 – Mathematical Logic I
  • PHIL 5307 – Logic
  • PHIL 5311 – Properties of Formal Systems
  • PHIL 5344 – Seminar in Philosophical Logic