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Musical Doughnut.

The topology of the syntonic temperament's tonnetz is generally cylindrical. Any syntonic "equal" tuning (i.e., a tempered width of the perfect fifth which divides the octave into a number of equally-wide intervals) snaps this cylinder into a torus(the shape of a ring doughnut, a hula hoop or an inflated tire), showing that it has a topology equivalent to S1×S1.

Wikipedia: Tonnetz