Give an explicit description of the covering space of the torus corresponding to the subgroup of generated by .

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- December 1st 2011, 02:19 PMkierkegaardCovering space
Give an explicit description of the covering space of the torus corresponding to the subgroup of generated by .

- December 1st 2011, 07:39 PMDrexel28Re: Covering space
You know that the universal cover of is and consists of translations by elements of the lattice . Your subgroup corresponds to the subgroup consisting of . Your covering space then corresponds to the quotient , where (as I hope you know) this means that if they differ by a -action.

- December 1st 2011, 08:03 PMkierkegaardRe: Covering space
- December 1st 2011, 08:06 PMDrexel28Re: Covering space
- December 1st 2011, 08:36 PMkierkegaardRe: Covering space
Wait, I'm a little confused. It's a cylinder, isn't it? If we consider the relation and the quotient map , the image of is a cylinder identifying a pair of opposite sides of a square. I hope to be right.

- December 1st 2011, 09:42 PMDrexel28Re: Covering space
Right! Intuitively what we've done is decomposed ( and ) which induces a decomposition (where are the deck transformation and respectively). Intuitively you can think then of as where the identifcation (our identification) corresponds to taking and wrapping it around itself (horizontally) to get a cylinder, and then modding by gives you the vertical identifications giving us the torus.

So, in short, yes. It's the cylinder.