In reply to  Jürg Wyttenbach's message of Thu, 17 Sep 2020 23:22:05 +0200:
Hi Jürg,

If you are talking about a torus, then it would help if you make a distinction 
between major and minor radius.

>Things are tricky:
>A torus diameter is 4R ! But the torus radius is only R! So its a matter 
>of perspective.

No, it's a matter of stating exactly what you mean, and leaving nothing to the 
imagination. ;) (Because one person will
often imagine something completely different to someone else, given the same 
"shorthand" description.)

I assume you are assuming a torus with a central hole that is zero in size. In 
which case the major radius is twice the
minor radius.

>If you look at the same distance circle radius "torus 2 radii" then the 
>4D radius - seen in 3D -  is longer!

Does this mean "the 4D radius is longer than the 3D radius", or the "3D radius 
is longer than the 4D radius", or "the
circumference of ... is longer than that of ...." or "some distance is longer 
than some other distance"?

As you can see, I don't like ambiguity. ;)

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