manual

62
How to do it:
1) Tie your wrists loosely.
2) Slip a hand inside the circle and
make it slip down between the wrist
and the cord, as in the picture.
3) Move the circle from your arm over your hand and the cord, and
then take it half way along the cord.
The trick you have just tried belongs
to a branch of modern mathematics
that is interested in how shapes can
roll, move, and change into different
shapes. This branch is called topology,
the geometr
y of distor
tion (sometimes
called “rubber sheet geometry”).
The operation in reverse gives
you the answer to the pr
oblem.
Notice that the soft foam circle is flexible.