This commit is contained in:
parent
72025f8ea8
commit
fc4f57a8b0
2 changed files with 4 additions and 3 deletions
|
@ -144,8 +144,9 @@
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Consider $(F, \cT\defon{F})$ and $(X \setminus F, \cT\defon{X \setminus F})$.
|
Consider $(F, \cT\defon{F})$ and $(X \setminus F, \cT\defon{X \setminus F})$.
|
||||||
Both are Polish spaces.
|
Both are Polish spaces.
|
||||||
Take the coproduct\footnote{topological sum} $F \oplus (X \setminus F)$
|
Take the coproduct%
|
||||||
of these spaces.
|
\footnote{In the lecture, this was called the \vocab{topological sum}.}
|
||||||
|
$F \oplus (X \setminus F)$ of these spaces.
|
||||||
This space is Polish,
|
This space is Polish,
|
||||||
and the topology is generated by $\cT \cup \{F\}$,
|
and the topology is generated by $\cT \cup \{F\}$,
|
||||||
hence we do not get any new Borel sets.
|
hence we do not get any new Borel sets.
|
||||||
|
|
|
@ -26,7 +26,7 @@
|
||||||
Let $X$ be a Polish space.
|
Let $X$ be a Polish space.
|
||||||
A set $A \subseteq X$
|
A set $A \subseteq X$
|
||||||
is called \vocab{analytic}
|
is called \vocab{analytic}
|
||||||
if
|
iff
|
||||||
\[
|
\[
|
||||||
\exists Y \text{ Polish}.~\exists B \in \cB(Y).~
|
\exists Y \text{ Polish}.~\exists B \in \cB(Y).~
|
||||||
\exists \underbrace{f\colon Y \to X}_{\text{continuous}}.~
|
\exists \underbrace{f\colon Y \to X}_{\text{continuous}}.~
|
||||||
|
|
Loading…
Reference in a new issue