Among other things, Christopher James Huff wrote:



>> has a definite inside and outside (when in the surface of the torus).
> 
> It is two-sided...I don't know if that's a requirement for it to be a

> but that page kind of contradicts itself, giving a definition of a


> there's not really any other differences between the shapes. I think
> it's close enough, though...

For me it is an important difference, but I'm no one in Mathematics :-) 

it strange in some way; a strip with an odd number of half-twists is 

with an even number of half-twists is just a twisted strip, there's nothing 
strange about it. Well, that's my view, I wouldn't say an "open" cylinder 


-- 
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