Usually they are referred to as "Klein bottles," and when pictured are pictured as closed. Indeed, it is pretty hard to draw one any other way. The mouth of the bottle passes through the body of the bottle and then comes around. It is the three dimensional equivalent of a Mobius strip, which has only one side.
BTW, Maurits Escher's picture, The Picture Gallery, is really a picture of a Klein bottle.
More nasty math, but of no social consequence whatsoever, and without any of the irony this list is well known for... Barkley Rosser -----Original Message----- From: Dennis Robert Redmond <dredmond at efn.org> To: lbo-talk at lists.panix.com <lbo-talk at lists.panix.com> Date: Friday, February 16, 2001 9:54 PM Subject: Re: Tasteless site
>On Mon, 12 Feb 2001, W. Kiernan wrote:
>
>> I suppose some folks have actually never heard of Klein jars.
>
>There's actually a mention of Klein space in "Evangelion", but I didn't
>realize it was an actual mathematical concept until this thread. Who says
>anime can't be educational!
>
>-- Dennis
>
>