Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Let the centers of a finite number of disjoint, closed disks be pinned to the plane, but with each free to rotate about its center. Given an arrangement of such disks with each labeled + or -, we investigate the question of whether they can be all wrapped by a single loop of string so that, when the string is taut and circulates, it rotates by friction all the ⊕-disks counterclockwise and all the ⊖-disks clockwise, without any string-rubbing conflicts. We show that although this is not always possible, natural disk-separation conditions guarantee a solution. We also characterize the hexagonal "penny-packing" arrangements that are wrappable.
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O'Rourke, Joseph, "String-Wrapped Rotating Disks" (2012). Computer Science: Faculty Publications, Smith College, Northampton, MA.