Today, with my bright topology 9th-graders, we discussed homotopy equivalence of spaces and the fundamental groupoid. In order to get the arguments sorted out, and also in order to give my esteemed readership a chance to see what I’m doing with them, I’ll write out some of the arguments here.
I will straight off assume that continuity is something everyone’s comfortable with, and build on top of that.
Homotopies and homotopy equivalences
We say that two continuous maps, f,g:X→Y between topological spaces are homotopical, and write , if there is a continuous map such that H(x,0)=f(x) and H(x,1)=g(x). This captures the intuitive idea of step by step nudging one map into the other in formal terms.
Two spaces X,Y are homeomorphic if there are maps , such that and .
Two spaces X,Y are homotopy equivalent if there are maps , such that and .