4
$\begingroup$

I recently isolated the following definition, which I believe it should have appeared somewhere.

Let $\kappa$ be a cardinal, and let $X$ be a set with $\kappa^+\leq |X|$.

Definition: An ideal $\mathcal I\subseteq \mathcal P(\mathcal P_{\kappa^+}(X))$ is called a B-ideal if the following hold.

  1. for every $x\in X$, $\{A\in \mathcal P_{\kappa^+}(X):x\in A \}$ is not in $\mathcal I$.
  2. $(\mathcal I^{+},\subseteq)$ has a $\kappa$-closed dense subset which means there is $\mathcal D\subseteq \mathcal I^+$ such that for every $A\in\mathcal I^+$, there is $B\in\mathcal D$ with $B\subseteq A$, and that every decreasing sequence in $\mathcal D$ of length less than $\kappa$ has a lower bound.

In my definition B stands for Baumgartner.

My question is if such an ideal has a name in the litrature?

$\endgroup$
4
  • 1
    $\begingroup$ @GabeGoldberg I clarified the notion of closedness. $\endgroup$
    – Rahman. M
    Commented Dec 23, 2020 at 11:38
  • 1
    $\begingroup$ I don’t think it has a name, but the hypothesis appears in the literature. See for example, Proposition 5.22 in Foreman’s chapter of the Handbook of Set Theory. $\endgroup$ Commented Dec 25, 2020 at 10:22
  • 2
    $\begingroup$ A very similar hypothesis also appears as Lemma 4.5 in my thesis. $\endgroup$ Commented Dec 25, 2020 at 10:57
  • $\begingroup$ Thank you @MonroeEskew . $\endgroup$
    – Rahman. M
    Commented Dec 25, 2020 at 11:59

0

You must log in to answer this question.

Browse other questions tagged .