David Fernández Bretón earned a Ph.D. from the Department of Mathematics and Statistics of York University in Toronto, under the supervision of Juris Steprāns.

My main interests are Logic and Set Theory, especially Forcing and Large Cardinals (although my knowledge of the latter is not as deep as I would like), and their applications to Algebra and Analysis. I am currently working on the algebra and topology of the Stone-Čech compactification of groups, notably Abelian groups, and with idempotents in said compactification. I have also been interested in the Cardinal Invariants of the Continuum for a while.

In a much more informal fashion (pretty much as a hobby), I also like to look at alternative axiomatizations of set theory, such as NFU, and some (very basic) category theory. I am also interested in the Philosophy of Mathematics and in Ludwig Wittgenstein’s life and work.

Personal website

# Recent and upcoming talks by David J. Fernández Bretón

## David J. Fernández Bretón: mathfrak p=mathfrak t, III

Tuesday, April 18, 2017, from 4 to 5:30pm East Hall, room 3096 Speaker: David J. Fernández Bretón (University of Michigan) Title: mathfrak p=mathfrak t, III Abstract: This is the third and last talk in the series (reasonably self-contained for those who missed any number of previous parts). continue reading…

## David J. Fernández Bretón: mathfrak p=mathfrak t, II

Thursday, April 6, 2017, from 4 to 5:30pm East Hall, room 3088 Speaker: David J. Fernández Bretón (University of Michigan) Title: mathfrak p=mathfrak t, II Abstract: This is the second in a series of (hopefully at most) three talks, and it will be reasonably self-contained for those who missed the first part. continue reading…

## David J. Fernández Bretón: mathfrak p=mathfrak t

Thursday, March 30, 2017, from 4 to 5:30pm East Hall, room 3088 Speaker: David J. Fernández Bretón (University of Michigan) Title: mathfrak p=mathfrak t Abstract: In a series of (hopefully at most) two talks, I will present the proof, due to Maryanthe Malliaris and Saharon Shelah in 2012, that the cardinal invariants p and t are equal, which constitutes an extremely important result in the theory of Cardinal Characteristics of the Continuum. continue reading…

## David Fernández Bretón: Strong failures of higher analogs of Hindman’s theorem, IV

Thursday, November 3, 2016, from 4 to 5:30pm East Hall, room 3096 Speaker: David Fernández Bretón (University of Michigan) Title: Strong failures of higher analogs of Hindman’s theorem, IV Abstract: This is talk 4 out of 4. continue reading…

## David J. Fernández Bretón: Strong failures of higher analogs of Hindman’s theorem, III

Thursday, October 27, 2016, from 4 to 5:30pm East Hall, room 3096 Speaker: David J. Fernández Bretón (University of Michigan) Title: Strong failures of higher analogs of Hindman’s theorem, III Abstract: Assuming the Continuum Hypothesis, Hindman, Leader and Strauss recently exhibited a colouring of the real line with two colours such that, for every uncountable set of reals, the collection of pairwise sums of these reals is panchromatic. continue reading…

## David J. Fernández Bretón: Strong failures of higher analogs of Hindman’s theorem, II

Thursday, October 20, 2016, from 4 to 5:30pm East Hall, room 3096 Speaker: David J. Fernández Bretón (University of Michigan) Title: Strong failures of higher analogs of Hindman’s theorem, II Abstract: (One of the versions of) Hindman’s theorem states that, whenever we partition an infinite abelian group G in two cells, there exists an infinite subset X of G such that the set FS(X) consisting of all sums of finitely many distinct elements of X is entirely contained within one of the cells of the partition. continue reading…

## David J. Fernández Bretón: Strong failures of higher analogs of Hindman’s theorem, I

Thursday, October 13, 2016, from 4 to 5:30pm East Hall, room 3096 Speaker: David J. Fernández Bretón (University of Michigan) Title: Strong failures of higher analogs of Hindman’s theorem, I Abstract: (One of the versions of) Hindman’s theorem states that, whenever we partition an infinite abelian group G in two cells, there exists an infinite subset X of G such that the set FS(X) consisting of all sums of finitely many distinct elements of X is entirely contained within one of the cells of the partition. continue reading…

## Set Theory and its Applications in Topology, September 11-16, 2016

The meeting took place in Oaxaca, Mexico. The slides may be found below. 08:45 – 09:00 Introduction and Welcome (Conference Room San Felipe) 09:00 – 10:00 Alan Dow: The even numbered problems (Conference Room San Felipe) 10:00 – 10:30 Rodrigo Jesus Hernandez Gutierrez: Spaces discretely generated at infinity (Conference Room San Felipe) 10:30 – 11:00 Coffee Break (Conference Room San Felipe) 11:00 – 11:30 Isván Juhász: Lindelöf spaces of countable pseudocharacter (Conference Room San Felipe) 11:30 – 12:00 Juris Steprans: PID and universal graphs (Conference Room San Felipe) 13:20 – 13:30 Group Photo (Hotel Hacienda Los Laureles) 13:30 – 15:00 Lunch (Restaurant Hotel Hacienda Los Laureles) 15:00 – 16:00 Itay Neeman: Forcing one instance of the Moore-Todorcevic principle (Conference Room San Felipe) 16:00 – 16:30 Coffee Break (Conference Room San Felipe) 16:30 – 17:00 James Cummings: Dowker and super-Dowker filters (Conference Room San Felipe) 17:00 – 17:30 Assaf Rinot: The $\omega_2$-Souslin problem (Conference Room San Felipe) 19:00 – 21:00 Dinner (Restaurant Hotel Hacienda Los Laureles) Tuesday, September 13 07:30 – 09:00 Breakfast (Restaurant at your assigned hotel) 09:00 – 10:00 Christina Brech: Bases of Homogeneous families bellow the first Mahlo cardinal (Conference Room San Felipe) 10:30 – 11:00 Coffee Break (Conference Room San Felipe) 11:00 – 11:30 Piotr Koszmider: A non-commutative Mrówka’s $\Psi$-space (Conference Room San Felipe) 11:30 – 12:00 Asger Tornquist: Invariant descriptive set theory and almost disjointness modulo an ideal (Conference Room San Felipe) 13:30 – 15:00 Lunch (Restaurant Hotel Hacienda Los Laureles) 15:00 – 16:00 Alexander Shibakov: Sequential groups: large and small (Conference Room San Felipe) 16:00 – 16:30 Coffee Break (Conference Room San Felipe) 16:30 – 17:00 Jindrich Zapletal: Strong measure zero sets in Polish groups (Conference Room San Felipe) 17:00 – 17:30 Marcin Sabok: On hyperfiniteness of boundary actions of hyperbolic groups (Conference Room San Felipe) 19:00 – 21:00 Dinner (Restaurant Hotel Hacienda Los Laureles) Wednesday, September 14 07:30 – 09:00 Breakfast (Restaurant at your assigned hotel) 09:00 – 09:30 Joerg Brendle: Q (Conference Room San Felipe) 09:30 – 10:00 Dilip Raghavan: More on the density zero ideal (Conference Room San Felipe) 10:00 – 10:30 Osvaldo Guzmán: Combinatorial properties of MAD families (Conference Room San Felipe) 10:30 – 11:00 Coffee Break (Conference Room San Felipe) 11:00 – 11:30 Victor Torres-Perez: Constructions with oppositions: Cardinal invariants and games (Conference Room San Felipe) 11:30 – 12:00 David Fernández Bretón: Strong failures of higher analogs of Hindman’s theorem (Conference Room San Felipe) 12:00 – 12:30 Natasha Dobrinen: Topological Ramsey spaces in some creature forcings (Conference Room San Felipe) 12:30 – 13:30 Lunch (Restaurant Hotel Hacienda Los Laureles) 13:30 – 17:30 Free Afternoon (Oaxaca) 19:00 – 21:00 Dinner (Restaurant Hotel Hacienda Los Laureles) Thursday, September 15 07:30 – 09:00 Breakfast (Restaurant at your assigned hotel) 09:00 – 10:00 Slawomir Solecki: Monoid actions on left-topological compact semigroups (Conference Room San Felipe) 10:30 – 11:00 Coffee Break (Conference Room San Felipe) 11:00 – 11:30 Aleksandra Kwiatkowska: The Ramsey degree of the pre-pseudoarc (Conference Room San Felipe) 11:30 – 12:00 Dana Bartosova: Ultrafilter combinatorics in topological dynamics (Conference Room San Felipe) 13:30 – 15:00 Lunch (Restaurant Hotel Hacienda Los Laureles) 15:00 – 16:00 Jan van Mill: Erdős spaces (Conference Room San Felipe) 16:00 – 16:30 Coffee Break (Conference Room San Felipe) 16:30 – 17:00 Anush Tserunyan: Topological dimension and Baire category (Conference Room San Felipe) 17:00 – 17:30 Yinhe Peng: Weak network and the basis problem (Conference Room San Felipe) 19:00 – 21:00 Dinner (Restaurant Hotel Hacienda Los Laureles) Friday, September 16 07:30 – 09:00 Breakfast (Restaurant at your assigned hotel) 09:00 – 09:30 Jeffrey Bergfalk: Walks… (Conference Room San Felipe) 09:30 – 10:00 Iian Smythe: A local Ramsey theory for block sequences (Conference Room San Felipe) 10:00 – 10:30 Noé de Rancourt: Ramsey theory with and without the pigeonhole principle (Conference Room San Felipe) 10:30 – 11:00 Coffee Break (Conference Room San Felipe) 11:00 – 11:30 Claribet Piña: Topological partition relations for $\omega^2$ (Conference Room San Felipe) 11:30 – 12:00 Carlos Uzcategui: Bases and selectors for cofinal families of countable sets (Conference Room San Felipe) 12:00 – 12:30 Carlos Di Prisco: Graphs on the Cantor set (Conference Room San Felipe) 12:30 – 14:30 Lunch (Restaurant Hotel Hacienda Los Laureles)   continue reading…

## David Fernández Bretón: Ultrafilters on the rationals generated by perfect sets

Place: Fields Institute (Room 210) Date: June 17th, 2016 (13:30-15:00) Speaker: David Fernandez Bretón Title: Ultrafilters on the rationals generated by perfect sets Abstract:  In a 1992 paper, van Douwen defined what he calls a “gruff ultrafilter”: an ultrafilter on the rational numbers which is generated by perfect (this is, closed and crowded) sets; and asked whether these ultrafilters exist, providing in the same paper a proof that they do if cov(M)=c. continue reading…

## David Fernández Bretón: d=c implies that there are gruff ultrafilters

Thursday, February 25, 4:00-5:30 PM at CC Little 2502 (note the nonstandard building/room!!!) I will show a proof of the statement in the title. Recall that a gruff ultrafilter was defined by van Douwen to be an ultrafilter on the rational numbers with a base of perfect subsets (where perfect means both closed (in the topology inherited from the usual Euclidean one from the reals) and crowded (without isolated points)). continue reading…