A general approach to pointfree \(T_0\) spaces
 
 
Description: 

The classical dual adjunction between frames and spaces, given by the functors \( O\colon \mathbf{Top}\to\mathbf{Frm} \) and \( \mathsf{pt}\colon\mathbf{Frm}\to\mathbf{Top} \), restricts to a dual equivalence between sober spaces and spatial frames. Another pointfree approach to the study of spaces is the so-called \( T_D \) duality, a similar dual adjunction where the fixpoints are the \( T_D \) spaces. The two dualities are incompatible in that the two spectrum functors are different. Recently, a pointfree approach to spaces whose fixpoints are all \( T_0 \) spaces was introduced. The approach is inspired by Raney duality. In this setting, we study the category of Raney extensions and show that we have a dual adjunction extending \( (O,\mathsf{pt}) \) and capturing all \( T_0 \) spaces. By suitably restricting on objects we recover both the classical and the \( T_D \) duality. Other pointfree notions of \( T_0 \) spaces are given by strictly zero-dimensional biframes and McKinsey-Tarski algebras. Aiming to understand the relationship between these three different settings, we introduce and study an abstract notion of pointfree \( T_0 \) space. We study the situation where we have a suitable forgetful functor \( U\colon\mathcal C\to\mathbf{Frm} \) and a dual adjunction \( O_\mathcal C\colon \mathbf{Top}\to\mathcal C \) and \( \mathsf{pt}_\mathcal C\colon \mathbf{Top} \to\mathcal C \) whose fixpoints are the \( T_0 \) spaces and which is, in a sense that will be made precise, compatible with the adjunction \( (O,\mathsf{pt}) \) between frames and spaces. By studying the fibers of \( U \), we are able to study various aspects of \( T_0 \) spaces abstractly. In all pointfree notions of \( T_0 \) spaces mentioned above, the pointfree sober spaces are the top elements of the fibers, and the \( T_D \) ones are the bottom elements.

Date:  2025-08-19
Start Time:   12:00
Speaker:  Anna Laura Suarez (Univ. Western Cape, South Africa)
Institution:  University of the Western Cape, South Africa
Place:  Online: https://teams.microsoft.com/l/meetup-join/19%3ameeting_NmE4NDNlOTUtM2Y0ZC00MzdiLWJkNTMtMDVjNDdhMmJmMDc2%40thread.v2/0?context=%7b%22Tid%22%3a%22d72758a0-a446-4e0f-a0aa-4bf95a4a10e7%22%2c%22Oid%22%3a%22bb01918f-9910-4e5d-8822-5175e49e8181%22%7d
Organization:  Fernando Lucatelli Nunes
Research Groups: -Algebra, Logic and Topology
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