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Continuum theory, point-set topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

10 votes
2 answers
426 views

Two questions about the "grasp" cardinal function

For a topology $\mathcal{T}$ on a set $S$, where $\mathcal{T}$ does not have a finite base, I define the grasp $g(\mathcal{T})$ to be the least infinite cardinal $\kappa$ such that $\mathcal{T}$ has a …
DanielWainfleet's user avatar
2 votes
1 answer
197 views

If $S$ is non-stationary in $[k]^{\omega}$ is there a choice-function on $S$ with bounded fi...

Fodor's Lemma : When $k$ is a regular uncountable cardinal, and $T$ is a stationary subset of $k$, any regressive $f:T\to k$ has a fiber which is stationary in $k$. Corollary: $T$ is stationary in $ …
DanielWainfleet's user avatar
10 votes
1 answer
329 views

Possible cardinalities of the remainders of compactifications of $\Bbb R$

With the usual topology on $\Bbb R$, a compactification $\mathrm{id}_{\Bbb R}:\Bbb R\to v\Bbb R$ can have a remainder $v\Bbb R \setminus \Bbb R$ of cardinality $1,2, 2^{\aleph_0}=\mathfrak c,$ or $2^{ …
DanielWainfleet's user avatar