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Since W is countable, we cannot hope to prove W is connected.
We prove instead
that is connected.
First we need some topological lemmas.
Give the discrete topology and the product topology,
as usual.
If is a finite vector of 0's and 1's, let
be the set of sequences in
which start with v.
The following lemma is the key ingredient in the connectivity proof.
Lemma 4.1
Let Y be a topological space.
Suppose is a continuous map such that
for all , and all .
(Here v0 denotes the vector v with 0 appended, etc.)
Then the image of f is path connected.
Let M be a topological space.
Give the product topology and let the symmetric group act on
by permuting the coordinates.
The space , which parameterizes n-element multisets, can be
given the quotient topology.
Lemma 4.2
If is connected, and the multiset is in A for some , then the subset of all coordinates of points in A is connected.
Theorem 4.1
is connected.
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