A Shelah group in ZFC
Speaker:
Mark Poor, Hebrew University of Jerusalem
Date and Time:
Friday, May 12, 2023 - 1:30pm to 2:30pm
Location:
Fields Institute, Room 210 or online at https://zoom.us/j/92415047239
Abstract:
In a paper from 1980, Shelah constructed a Jonsson group of
size Aleph_1.
Assuming CH, he moreover obtained what is now known as a
"Shelah group" of size Aleph_1, i.e., a group of size Aleph_1 such that
for some integer N, the collection of all N-sized words over the
alphabet of any given uncountable subset of the group resurrects the
whole group.
In this talk, we shall present a ZFC construction of a Shelah group at
the level of any successor of a regular cardinal. We shall also address
the problem of constructing Shelah groups at successors of singulars and
at inaccessibles.