Re: On the appendix of Allen Hatcher's book "Algebraic Topology"(2001)

From: Nobuo Saito (genkisaito_at_hotmail.com)
Date: 11/02/04 

Date: 1 Nov 2004 19:03:21 -0800

Robin Chapman <rjc@ivorynospamtower.freeserve.co.uk> wrote in message news:<cllr2t$o3m$1@south.jnrs.ja.net>...
> Nobuo Saito wrote:
>
> >>
> >> What I think one needs is that N^{n+1}(A) union A deformation
> >> retracts onto N^n(A) union A.
> >
> > That's about it. You need shrinking neighborhoods to A.
>
> Yes, but a deformation retraction from N^{n+1}(A) to N^n(A)
> extends uniquely to one from N^{n+1}(A) u A to N^n(A) u A.

First, you need to prove N^{n+1}(A) deformation retracts onto N^n(A).