I was trying to show that the Klein bottle was second countable. My try was to use that it has the subspace topology of $\mathbb R^3$. Then I noticed that it is not imbeddable into $\mathbb R^3$. Therefore one cannot use the subspace topology. But I don’t know what else to do. How to show […]

First of all, I am aware of the question in How to embed Klein Bottle into $R^4$ , which was inconclusive. Anyway, I’ve made some progress, but I still have a question. I am using Do Carmo’s Riemannian Geometry, and struggling to solve a problem. The problem is: Show that the mapping $G:\mathbb{R}^2\to\mathbb{R}^4$ given by […]

Consider the Klein bottle (this can be done by making a quotient space). I want to give a proof of the following statement: The Klein Bottle is homeomorphic to the union of two copies of a Möbius strip joined by a homeomorphism along their boundaries. I know what such a Möbius band looks like and […]

I know that in general, $H_{n}(X)$ counts the number of $n$-cycles that are not $n$-boundaries of a simplicial complex $X$. So for the sphere, $H_{0}(X) \cong \mathbb{Z}$ since it is connected. Also $H_{n}(X) = 0$ for all $n>0$ (e.g. all $1$-cycles are $1$-boundaries, etc..). How do you use this geometric interpretation to deduce that $H_{1}(X) […]

Does the concept of a Möbius torus make sense: taking a cylinder (instead of a rectangle as in the case of the Möbius strip) and twisting it before joining its ends? Or will the resulting twisted torus be indistinguishable from the normal torus in any relevant respect? [This equivalent to the well-known Möbius strip should […]

I want to calculate the Klein bottle. So I did it by Van Kampen Theorem. However, when I’m stuck at this bit. So I remove a point from the Klein bottle to get $\mathbb{Z}\langle a,b\rangle$ where $a$ and $b$ are two loops connected by a point. Also you have the boundary map that goes $abab^{-1}=1$, […]

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