In this research seminar we will treat two-cardinal problems. Shelah's historic forcing, Todorcevic's rho-functions, and morasses have been applied successfully in this area, but there are still many open problems. Our starting point is the first result in this area solved by Shelah using historic forcing. Then we look at the other methods which have been applied in this field and we look at some open problems.
Abstract An introduction to two-cardinal problems: A sketch of the forcing construction of [1].
Abstract How to use Shelah's historic forcing to get a function with property delta
Abstract Continuation of Historic forcing I.
Abstract Continuation of Historic forcing I.
Abstract Using historic forcing we can get a function with property delta. In this session we see how to get a forcing extension with a superatomic algebra from this assumption.
Abstract Using coherent sequences and Todorcevic's minimal walks we can define the function Rho. In this session we define coherent sequences, minimal walks, and the function Rho. Then we show some of its basic properties, in particular its subadditivity.
Abstract Continuation of the previous talk.
Abstract We interpret the function rho in terms of Aronszajn trees.
Abstract We prove the unboundedness property of rho. This is used to construct a forcing that adds a function f: omega_2 x omega_2 --> omega that is not constant on any rectangle with infinite sides.
Abstract Continuation of the previous talk.
Abstract Using the rho-function, we define a function D and prove that it has property Delta.
Abstract Continuation of the previous talk.
Abstract Using a function with property Delta, we construct a ccc forcing that adds a Kurepa tree.