is connected.
First we show that for,
![]()
is connected. The idea is to apply Lemma 4.1 to the function f which assigns to
the set of zeros of
![]()
inside
. To make a continuous map of this requires some manipulation.
By Jensen's theorem, as was shown in Section 2, there is an upper bound n on the number of zeros that a power series with 0,1 coefficients can have inside
. Let M be
with the annulus
shrunk to a point P. (Therefore M is topologically a sphere.) To each power series
,
, we assign the set of zeros inside
, (counted with multiplicities) and throw in extra copies of the point P as necessary to bring the total number of points to n. Since the order of these n elements of M is unspecified, we obtain a point of
. Let
be this point.
We claim that this map
![]()
is continuous. This follows easily from Rouché's theorem; if two power series agree in the first m coordinates for m sufficiently large then their zeros inside
will be within
. Some may escape or enter the disk, but this is not a problem, since in the topology on M, P is close to all points z with |z| sufficiently near
.
We next check condition
of Lemma 4.1. This is easily done using the following trick: given
, let
. Then
,
, and
(we extend v,w to infinite vectors by appending 0's), since
![]()
and
![]()
have the same zeros inside
. Therefore we may apply Lemma 4.1 and deduce that the image of f is path connected.
Since
, we may apply Lemma 4.2 with
to deduce that
with the annulus
shrunk to a point P is a connected subset of M. This is equivalent to the connectivity of
.
Since
is the decreasing intersection of the compact connected sets
, it too is connected. So is its image under
. Finally,
is the union of these two sets, which meet on the unit circle, so
is connected as well.