From Monica Lee, Lancaster University
I enjoyed your article on knitting Klein bottle hats
(22/29 December, p 38),
although I think it is a bit much to claim they have only just been invented by
Cliff Stoll, since I have been making them for family and friends since the
early 1970s—but perhaps not many people knew that.
My reason for writing, however, is not to lay claim to ownership of the idea
but to point out an interesting quirk of the knitted Klein bottle. When knitted
with horizontal stripes everything matches up nicely, but when the stripes are
vertical it becomes obvious that the surfaces, although they join together
neatly, are transposed.
