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Re:Gboard Double Sided Version by i2go on Thursday October 10, 2024 @09:22AM (#41798525)
is it? isn’t a coffee cup equivalent to a torus? which is not equivalent to a mobius strip
Re:Gboard Double Sided Version by verdverm on Thursday October 10, 2024 @11:25AM (#41799837)
torus and mobius strip are both genus 1

imagine inflating the mobius strip like a long balloon, so that it loses the edge

Re:Gboard Double Sided Version by carltg_ on Thursday October 10, 2024 @02:08PM (#41801518)
The genus is insufficient to determine if an object is equivalent to the other. Orientability distinguishes the mobius strip and the torus, a torus is orientable whereas a mobius strip is not. Therefore, topologically speaking they are not equivalent.
Re:Gboard Double Sided Version by verdverm on Thursday October 10, 2024 @03:38PM (#41802656)
What is orientability? Why is the torus able but not the mobius strip?
Re:Gboard Double Sided Version by verdverm on Thursday October 10, 2024 @03:41PM (#41802688)
Re:Gboard Double Sided Version by i2go on Thursday October 10, 2024 @08:00PM (#41804810)
you can make a mobius strip with paper. then get a pencil and try to orient it in the mobius strip. that is, make it normal to the paper then move it around. you will see that if you go though the strip and go back to the starting point the pencil will be in the other direction. thus, the orientation is not continuous so the surface is not orientable