If
then
is a point and
is homeomorphic to
and
the result is true in this case. The proof now proceeds by induction on
. Assume that the
result has been proved for
and let
be a homeomorphism. Define the
halves
and
as
and note that
is homeomorphic to the cube
. We construct the sets
and
, and use the Mayer Vietoris sequence to the
following open cover
of
:
Since
is homeomorphic to
, by induction hypothesis the end terms of the portion
are zero if
whereas the left most group is zero if
. In any case
is injective.
Assume that for some
,
. We choose
,
and
it follows
or
. Let us assume
that
. Since
is homeomorphic to
, the process can be repeated
subdividing
into two pieces whose intersection is homeomorphic to
. Thus we construct a
nested sequence of subsets
such that for each
,
the map
induced by inclusion, maps
to a non zero element.
Composing with
one checks that
for
,
thereby providing a map
Since the intersection
is homeomorphic to
, by induction hypothesis,
. Hence
for every
and hence by theorem (40.2) (ii),
for some
,
which is a contradiction.
Turning to the case
, assume that rank of
is atleast two. If we select points
and
lying in distinct path components of
, the cycle
in
is not a boundary.
As before we construct a nested sequence of compact sets
with
for each
. But since
has only one path component,
is a boundary where
is the map induced by the inclusion
whence
by (41.3). This in turn forces
by theorem (40.2) (ii) and we have a contradiction.
nisha
2012-03-20