Cuts in Hyperfinite Time Lines
Jin, Renling
J. Symbolic Logic, Tome 57 (1992) no. 1, p. 522-527 / Harvested from Project Euclid
In an $\omega_1$-saturated nonstandard universe a cut is an initial segment of the hyperintegers which is closed under addition. Keisler and Leth in [KL] introduced, for each given cut $U$, a corresponding $U$-topology on the hyperintegers by letting $O$ be $U$-open if for any $x \in O$ there is a $y$ greater than all the elements in $U$ such that the interval $\lbrack x - y, x + y\rbrack \subseteq O$. Let $U$ be a cut in a hyperfinite time line $\mathscr{H}$, which is a hyperfinite initial segment of the hyperintegers. $U$ is called a good cut if there exists a $U$-meager subset of $\mathscr{H}$ of Loeb measure one. Otherwise $U$ is bad. In this paper we discuss the questions of Keisler and Leth about the existence of bad cuts and related cuts. We show that assuming $\mathbf{b} > \omega_1$, every hyperfinite time line has a cut with both cofinality and coinitiality uncountable. We construct bad cuts in a nonstandard universe under ZFC. We also give two results about the existence of other kinds of cuts.
Publié le : 1992-06-14
Classification: 
@article{1183743971,
     author = {Jin, Renling},
     title = {Cuts in Hyperfinite Time Lines},
     journal = {J. Symbolic Logic},
     volume = {57},
     number = {1},
     year = {1992},
     pages = { 522-527},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1183743971}
}
Jin, Renling. Cuts in Hyperfinite Time Lines. J. Symbolic Logic, Tome 57 (1992) no. 1, pp.  522-527. http://gdmltest.u-ga.fr/item/1183743971/