Dear Cheerful Logicians and Friends of Logic, Before the main announcements, a note about an event some of you might be interested in: this week's VICTR seminar, by Junyeol Kim is titled "Frege on Logic: The Truth-value True and Logic Qua the Science of Truth". The seminar is on Tuesday November 17 at 09:00 GMT-6. Since some of you may care to attend this talk, here is a link: https://waikato.zoom.us/j/93335339244?pwd=MnoyTVhIajB1SDh3YnpQTmtQa3lRQT09
Now to the week's events. There are five events to announce; one on Monday, two on Wednesday, and one each on Thursday and Friday. Supergroup Talk *Speaker: *Sankha S Basu *Title: *The Muchnik Topos *Time and Date: *Thursday, November 19 18:00 (GMT-6) *Link: * https://ksu.zoom.us/j/92161069478?pwd=c3ZjbWMraVZKSDhNeUk0Sk5JOG5QQT09 *Meeting ID: *921 6106 9478 *Passcode: *topos *Abstract: *Kolmogorov, in 1923, proposed a model for intuitionistic propositional logic called the Calculus of Problems. Although simple and natural, this model was non-rigorous. A rigorous version of this was given by Medvedev and Muchnik in the 1950's and '60's using the concept of Turing oracles. Thus started the study of mass problems and the reducibility notions between these. Sheaves over topological spaces as models for higher-order intuitionistic logic were studied independently. These models are also examples of elementary topoi. In this work, we have extended the Kolmogorov/Medvedev/Muchnik line of work to a model of intuitionistic higher-order logic that we call the Muchnik topos. The Muchnik topos may be described in brief as the category of sheaves of sets over the topological space consisting of the Turing degrees, where the Turing cones form a base for the topology. We have also introduced, within the Muchnik topos, a class of intuitionistic real numbers, different from the Dedekind and Cauchy reals. We call these the Muchnik reals. Disclaimer: Although the title and abstract include the words "topos/ topoi/ category", the talk will not involve any Category Theory. Talks by Other Groups: *Logic and Metaphysics Workshop *(CUNY) *Speaker: *Nick Stang (Toronto) *Title: *Hegel's Logic as Logic and as Metaphysics *Time and Date: *Monday, November 16th, 15:15 (GMT-6) *Link:* https://gc-cuny.zoom.us/j/93998581367?pwd=d0tWWlR0L3N2a2RVelJCSVRSVjE4UT09 *Meeting ID:* 939 9858 1367 *Passcode:* 936107 *Abstract: *In the Encyclopaedia Logic Hegel claims that logic “coincides with” metaphysics (§24). In this talk, I will explain why Hegelian logic (the science of thinking) is identical with metaphysics (the science of being). Along the way, I will also shed light on two of the most obscure aspects of Hegel’s logic: that it involves “movement” and that this movement works by the identification, and resolution, of contradictions. *Proof Theory Seminar* *Speaker: *Albert Visser *Title: *Fixed Points meet Löb's Rule *Time and Date: *Wednesday, November 18th, 03:00 GMT-6 *Link:* https://www.proofsociety.org/proof-theory-seminar/participate.html *Abstract: *The modal part of the work reported in this talk is in collaboration with Tadeusz Litak. For a wide class of theories we have the Second Incompleteness Theorem and, what is more, Löb's rule, also in cases where the third Löb Condition L3 *provable implies provably provable* (aka 4) fails. We will briefly indicate some examples of this phenomenon. What happens when we do have Löb's Rule but not L3? It turns out that we still have a lot. For example, the de Jongh-Sambin-Bernardi Theorem on the uniqueness of fixed points remains valid. So, e.g., Gödel sentences are unique modulo provable equivalence. On the other hand, explicit definability of fixed points fails. An arithmetical example of the non-explicit-definability of the Gödel sentence is still lacking. (I do have an arithmetical example where the Gödel sentence is equivalent to the consistency of inconsistency but not to consistency.) We discuss the relevant logic: the Henkin Calculus, to wit, K plus Löb's rule plus boxed fixed points. This logic turns out to be synonymous to the mu-calculus plus the minimal Henkin sentence, which expresses well-foundedness. So, results concerning the mu-calculus, like uniform interpolation, can be transferred to the Henkin Calculus. *IU Logic Seminar* *Speaker: *Very Flocke *Title: *Carnap and Quantified Modal Logic *Time and Date: *Wednesday, November 18 15:00 (GMT-6) *Link: * https://iu.zoom.us/j/95326399432?pwd=VmVUWGxHeG5KQjEzQVozb3pCRHJVZz09 *Meeting ID: *953 2639 9432 *Password: *Smullyan *Abstract: *Quine (1984) argues that quantification into modal contexts is meaningless. The today most popular response to this charge, following Kripke (1972), reduces modality to essence. Carnap (1947) offers an alternative response. He argues that variables in modal languages do not refer to individuals but to individual concepts, and thereby avoids essentialism. I further develop this view using the contemporary distinction between semantic values and assertoric contents, and show why, from Carnap’s perspective, Kripke’s (1972) examples do not in fact show that the necessary and the a priori can come apart. *OCIE and Claremont* *Speaker: *Brigitte Stenhouse (Open University) *Title: *Translating Laplace’s Mécanique Céleste in early 19th-century Great Britain *Time and Date: *Friday, November 20th 11:00 GMT-6 *Link: * https://pitzer.zoom.us/j/96937631191?pwd=RkZZKzQyT2Z3Y3B2OHk0Y0I3SzZMdz09 *Abstract: *One of the key texts held up as an example of the inferiority of British mathematics in the early nineteenth century was Pierre-Simon Laplace’s Traité de Mécanique Céleste. The work, published in five volumes between 1799 and 1825, was said to reduce the “whole theory of astronomy into one work” and to be incomprehensible to all but a handful of British readers (Playfair, 1808). By 1825 three partial English translations of Mécanique Céleste had been published, each with unique additions and amendments aiming to make the work accessible to a reader with a ‘British’ mathematical education. Nevertheless, in the late 1820s it was still felt that a good English translation was lacking, and two authors, the Scottish Mary Somerville and the American Nathaniel Bowditch, produced translations which differed widely in style both from each other and from their predecessors. By considering these five translations side by side, we will investigate how different perceived causes of the inferiority of British mathematics led to different methodologies of translation. Other Notes and Announcements: - *The Logic Supergroup has a YouTube channel!* Recordings of almost all talks are available at https://www.youtube.com/channel/UCqOAS8SHP-5nGjYEE2FE6xw If you are part of a member group, are recording talks, and would like the supergroup to host them, then let us know! We'd be happy to help. Yay for logic! -- Você está recebendo esta mensagem porque se inscreveu no grupo "LOGICA-L" dos Grupos do Google. Para cancelar inscrição nesse grupo e parar de receber e-mails dele, envie um e-mail para [email protected]. Para ver esta discussão na web, acesse https://groups.google.com/a/dimap.ufrn.br/d/msgid/logica-l/CAMTR992uUA2OGbyMa7%2B4oksfFncWh1MHuSZ94psvKxzWj_gQrQ%40mail.gmail.com.
