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9 changes: 8 additions & 1 deletion properties/P000207.md
Original file line number Diff line number Diff line change
Expand Up @@ -3,18 +3,25 @@ uid: P000207
name: Strongly collectionwise normal
aliases:
- Divisible
- Almost $2$-fully normal
refs:
- zb: "0046.16403"
name: Sur une problème de M. Dieudonné (Cohen)
- doi: 10.1090/S0002-9939-1981-0630058-4
name: Strong collectionwise normality and M. E. Rudin’s Dowker space (Hart)
- doi: 10.2307/1993026
name: Some Generalizations of Full Normality (M. J. Mansfield)
---

For each neighborhood $U$ of the diagonal $\Delta=\{(x,x)\mid x\in X\}$
in $X\times X$, there is a neighborhood $V$ of the diagonal such that
$V\circ V\subseteq U$.

Studied by Cohen in {{zb:0046.16403}}
In Theorem 2.6 of {{doi:10.2307/1993026}} this property was shown to be equivalent to
almost $2$-fully normal: each open cover $\mathcal U$ has an open almost $2$-star
refinement $\mathcal V$, that is $\mathcal{V}$ is a refinement of $\mathcal{U}$ and for any $x, y, z$ with $y, z\in \text{St}(x, \mathcal{V})$ there exists $U\in\mathcal{U}$ with $y, z\in U$.

Originally studied by Cohen in {{zb:0046.16403}}
(<http://gallica.bnf.fr/ark:/12148/bpt6k3186w/f290.image>),
where it was shown to be
strictly stronger than {P88}.
Expand Down
5 changes: 2 additions & 3 deletions spaces/S000138/properties/P000207.md
Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,7 @@ value: true
refs:
- doi: 10.1090/S0002-9939-1982-0671226-6
name: More on M. E. Rudin’s Dowker space (K. P. Hart)
- doi: 10.2307/1993026
name: Some Generalizations of Full Normality (M. J. Mansfield)
---

By theorem 2.2 of {{doi:10.1090/S0002-9939-1982-0671226-6}}, {S138} is $2$-fully normal, and so almost $2$-fully normal. By theorem 2.6 of {{doi:10.2307/1993026}}, it's strongly collectionwise normal.
By theorem 2.2 of {{doi:10.1090/S0002-9939-1982-0671226-6}},
{S138} is $2$-fully normal, and so {{P000207}}.