In the enigmatic Canon 1 a 2 from J.S.Bach's "Musical Offering"
(1747) (also known as "crab canon" or "canon cancrizans"), the manuscript
shows a single score, whose beginning joins with the end. This space is
topologically equivalent to a bundle of the line segment over the circle,
known as a Möbius strip. The simultaneous performance of the deeply
related forward and backward paths gives appearance to two voices, whose
symmetry determines a reversible evolution. A musical universe is built
and then is "unplayed" back into silence.