It is well-known and easy to prove that the variety of groups abstractly captures algebras of permutations under composition and inverse, that the variety of inverse semigroups capture algebras of partial injective functions under composition and inverse, and that the variety of semigroups abstractly capture the algebras of any of total functions, partial functions or binary relations under the operation of composition. In contrast to this, a landmark result of Hirsch and Hodkinson showing the undecidability of determining when a finite algebra is isomorphic to an algebra of binary relations under Tarski’s signature: the usual set theoretic Boolean operations, composition, converse and identity. This is a very rich signature, and it has subsequently been discovered that undecidability of representability begins in weaker signatures. This talk will survey some of the very extensive literature in this area, and an overview of the approaches to undecidability, possibly touching on some new results for one of the weakest known algebraic signature to experience undecidability of representability as binary relations.
Undecidability of representability as binary relations
Borel subgroup orbits of classical symmetric spaces are parametrized by families of signed involutions called clans, which provide a combinatorial model for studying questions related to Schubert calculus on symmetric spaces. For symmetric spaces of Hermitian type, clans are grouped into “sects” corresponding to Schubert cells of an associated Grassmannian variety, yielding a cell decomposition of the symmetric space and facilitating a combinatorial description of the closure (Bruhat) order on the orbits. This decomposition reveals coincidences of clans in the largest sect with other well-studied posets of matrix Schubert varieties. We further describe explicit bijections between clans for Hermitian type symmetric spaces and several other combinatorial families of objects, including certain rook placements, set partitions, and weighted Delannoy paths. (Based on joint work with Mahir Can and Ozlem Ugurlu.)
The Bruhat order on symmetric spaces
Oct. 19, 2021 4pm (Zoom)
Math Edu
Jess Ellis Hagman (Colorado State University)
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In this talk I will share my current research that addresses student success in STEM from a critical perspective. A critical perspective on student success means locating student challenges in STEM not within the students' themselves but within the systems at play, and that these systems are failing students not because they are broken but because they are functioning perfectly well based on their design. I will share my research teams' current work focused on student experiences in college precalculus and calculus from a critical perspective, discussing both recent qualitative research and quantitative research studies. I care about these courses personally because I think the content is fun, but more importantly because of the role they play in STEM students' college experiences. This talk is intended for a broad audience to gain a new perspective on student success in STEM and learn a bit about research coming from this perspective.
Speaker bio: Jess Ellis Hagman is an Associate Professor in the Department of Mathematics at CSU. She completed her PhD in Mathematics Education from the joint program between San Diego State University and the University of California, San Diego. Her area of research is undergraduate mathematics education. Her work is focused on dramatically increasing the number and diversity of people who succeed in undergraduate mathematics-especially introductory mathematics courses that often function as a roadblock for STEM intending students. Her current research includes studying characteristics of successful precalculus and calculus programs, focusing on investigating ways departments can create diverse, equitable, and inclusive introductory mathematics programs.