SARAH MERZ, UNIVERSITY OF THE PACIFIC
In 1979, Frank Rubin posed the following puzzle in Recreational Mathematics: Professor X who is blind, keeps keys on a circular ring. Suppose there are a variety of handle shapes available that can be distinguished by touch. How many shapes does professor X need to use in order to keep n keys on the ring and still be able to select the proper key by feel? Generalized as a graph theory problem, this puzzle has been well studied. We will discuss this problem as viewed in the setting of directed graphs.
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