3 papers
math.LO2026
-Ramsey ultrafilters
José Antonio Corona-García, David José Fernández-Bretón, Ulises Ariet Ramos-García
We study -Ramsey ultrafilters, ultrafilters containing witnesses to every shift-invariant instance of Ramsey's theorem. We prove that it is consistent that there are no…
math.LO2024
Every Polish group has a non-trivial topological group automorphism
Carlos Pérez Estrada, Ulises Ariet Ramos-García
We prove that every Polish group with more than two elements admits a non-trivial topological group automorphism. As a consequence, a hypothetical uniquely homogeneous Polish space…
math.GN2020
Countably compact groups without non-trivial convergent sequences
Michael Hrušák, Jan van Mill, Ulises Ariet Ramos-García +1
We construct, in , a countably compact subgroup of without non-trivial convergent sequences, answering an old problem of van Douwen. As a consequen…