On versions of $\clubsuit$ on cardinals larger than $\aleph_1$

by Dzamonja and Shelah. [DjSh:685]
Math Japonica, 2000
We give two results on guessing unbounded subsets of lambda^+ . The first is a positive result and applies to the situation of lambda regular and at least equal to aleph_3, while the second is a negative consistency result which applies to the situation of lambda a singular strong limit with 2^lambda > lambda^+ . The first result shows that in ZFC there is a guessing of unbounded subsets of S^{lambda^+}_lambda . The second result is a consistency result (assuming a supercompact cardinal exists) showing that a natural guessing fails. A result of Shelah in [Sh:667] shows that if 2^lambda = lambda^+ and lambda is a strong limit singular, then the corresponding guessing holds. Both results are also connected to an earlier result of D{z}amonja-Shelah in which they showed that a certain version of clubsuit holds at a successor of singular just in ZFC. The first result here shows that a result of [DjSh:545] can to a certain extent be extended to the successor of a regular. The negative result here gives limitations to the extent to which one can hope to extend the mentioned D{z}amonja-Shelah result.


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