[logic-ml] 東北大ロジックセミナーのご案内(6月9日)

[YOKOYAMA Keita]

皆様，

東北大学の横山です．
以下の通りセミナーを開催いたしますのでご案内いたします．

https://sites.google.com/view/sendai-logic/

日時：6月9日(金)15:00〜
場所：東北大学理学研究科合同A棟801号室 (zoom配信あり)

講演者：Paul Shafer (University of Leeds)

Title: The Rival--Sands theorem for partial orders,
ascending/descending sequences, and Sigma_2 induction.

Abstract:
In their 1980 article, Rival and Sands proved two theorems inspired by
Ramsey’s theorem for pairs. The second of these theorems states that
every infinite partial order P of finite width contains an infinite
chain C with the property that every element of P is comparable either
with no element of C or with infinitely many elements of C. We show
that this theorem is equivalent to the ascending/descending sequence
principle plus the Sigma_2 induction scheme over RCA_0. This work is
joint with Marta Fiori-Carones, Alberto Marcone, and Giovanni Soldà.

どうぞよろしくお願いいたします．

横山啓太
--
Keita Yokoyama
Mathematical Institute, Tohoku University
Aoba, Sendai, JAPAN, 980-8578
keita.yokoyama.c2 at tohoku.ac.jp