We take
and
and note that
deformation retracts to
. Consider the portion of the Mayer Vietoris sequence
Since
and
are contractible spaces, we get for the case
,
and hence
(
).
By induction the result would follow as soon as we prove it for the case
.
For this case let us take a look at the
end of the Mayer Vietoris sequence:
Since
is injective,
To understand the map
we take a basis of
consisting of a pair of points
and
.
The singleton
generates
and
which is a boundary in
if and only if
.
Likewise
in
if and only if
. Thus the kernel of
is the infinite
cyclic group
generated by the zero chain
. Hence we get
To calculate 
for
we look at the portion of the Mayer Vietoris sequence
and observe that since
when
,
nisha
2012-03-20