A manifold is a surface that you can put a cd shaped object on in any place on the surface, you can change the radius of the cd but it has to have some radius above 0.

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snthpy 2 days ago | parent | next [-]

Nicely done!

Initially I recoiled at the thought of the stiffness of the CD, but of course your absolutely right, at least for 2d manifolds.

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BigTTYGothGF 2 days ago | parent | prev | next [-]

> you can put a cd shaped object on

You're thinking of open sets.

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BigTTYGothGF 2 days ago | parent [-]

In particular, consider two intersecting planes. You can put all the discs you like on that surface, but it's not a manifold because on the line of intersection it's not locally R2.

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dist-epoch 2 days ago | parent | prev [-]

Including the hole at the center of the CD?