# Definition:Hewitt's Condensed Corkscrew

## Contents

## Definition

Let $\omega$ be the first transfinite ordinal.

Let $\Omega$ be the first uncountable ordinal.

Let $\hointr 0 \Omega$ denote the set of countable ordinals.

Let $T = \struct {S, \tau}$ be the Tychonoff corkscrew:

- $S = C \cup \set {a^+} \cup \set {a^-}$

where $C$, $a^+$ and $a^-$ are as in that definition.

Let $A = T \times \hointr 0 \Omega$.

Let $S$ be the subset of $A$ consisting of $C \times \hointr 0 \Omega$.

Hence we can consider $A$ as being an uncountable sequence of Tychonoff corkscrews $A_\lambda$ where $\lambda \in \hointr 0 \Omega$.

Similarly, we can consider $S$ as being that same uncountable sequence of Tychonoff corkscrews missing all those distinguished points $a^+$ and $a^-$ at infinity.

Let $\Gamma: S \times S \to \hointr 0 \Omega$ be a bijection.

Let $\pr_i$ for $i \in \set {1, 2}$ be the projections from $S \times S$ to $S$.

Let us define the mapping $\psi: A \setminus S \to S$ by:

\(\displaystyle \map \psi { {a^+}_\lambda}\) | \(=\) | \(\displaystyle \pr_1 \map {\Gamma^{-1} } \lambda\) | |||||||||||

\(\displaystyle \map \psi { {a^-}_\lambda}\) | \(=\) | \(\displaystyle \pr_2 \map {\Gamma^{-1} } \lambda\) |

Then for $2$ distinct points $x, y \in S$, there exists some $\lambda \in \hointr 0 \Omega$, that is $\lambda = \Gamma {x, y}$, such that both $\psi^{-1} \sqbrk x$ and $\psi^{-1} \sqbrk y$ intersect $A_\lambda$.

The topology $\tau$ on $A$ is determined by the basis neighborhoods $N$ of each $x \in S$ with the property that:

- $\psi^{-1} \sqbrk {N \cap S} \subseteq N$

together with $A_\lambda$-basis neighborhoods called **tails** of each $a \in A \subseteq S$.

Hence $S$ will inherit the subspace topology from $A$.

A typical basis neighborhood of $x \in S$ is constructed as follows:

We begin by taking a $\sigma$-neighborhood $N_0$ of $x \cup \phi^{-1} \sqbrk x$ where $\sigma$ is the product topology on $A = T \times \hointr 0, \Omega$, where $\hointr 0, \Omega$ is given the discrete topology.

Then we define $N_i$ recursively as follows:

- $N_i$ is a $\sigma$-neighborhood of $N_{i - 1} \cup \psi^{-1} \sqbrk {N_{i - 1} \cap S}$

and:

- $N = \bigcup N_i$

Then $\psi^{-1} \sqbrk {N \cap S} \subseteq N$.

The topological space $\struct {S, \tau}$ so generated is referred to as **Hewitt's condensed corkscrew**.

## Also see

- Results about
**Hewitt's condensed corkscrew**can be found here.

## Source of Name

This entry was named for Edwin Hewitt.

## Sources

- 1978: Lynn Arthur Steen and J. Arthur Seebach, Jr.:
*Counterexamples in Topology*(2nd ed.): Part $\text {II}$: Counterexamples: $92$. Hewitt's Condensed Corkscrew