The Tree Property and uncountable cardinals

09/28/2022 12:30 pm - 1:30 pm
Alejandro Poveda Faidra Monachou Jie Wang Michael Simkin
CMSA Room G10
Address: CMSA, 20 Garden Street, Cambridge, MA 02138 USA

Colloquium

Speaker: Dima Sinapova (Rutgers University)

Title: The Tree Property and uncountable cardinals

Abstract: In the late 19th century Cantor discovered that there are different levels of infinity. More precisely he showed that there is no bijection between the natural numbers and the real numbers, meaning that the reals are uncountable. He then went on to discover a whole hierarchy of infinite cardinal numbers. It is natural to ask if finitary and countably infinite combinatorial objects have uncountable analogues. It turns out that the answer is yes.

We will focus on one such key combinatorial property, the tree property. A classical result from graph theory (König’s infinity lemma) shows the existence of this property for countable trees. We will discuss what happens in the case of uncountable trees.