Ken Baker, kb@math.gatech.edu
102 French Building, 404-385-7526

School of Mathematics
Georgia Institute of Technology
Atlanta, GA 30332-0160



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The three cyclic surgeries
of the
(-2,3,7) Pretzel knot




The (-2,3,7) Pretzel knot K may be obtained by Dehn surgery on the minimally twisted five chain link, MT5C. K will be the core of one of the surgery solid tori. It is also an embedded curve on the once-punctured torus fiber of the trefoil knot. Viewing this fiber as the plumbing of two Hopf bands, K may be obtained by Dehn twisting the first core twice about the second and then Dehn twisting this result twice about the original first core.

Quotienting each of these constructions by an involution, we may view the exterior of K as a ball containing a 2-string tangle as the fixed set of the involution. The presentation as a "punctured" 3-strand braid naturally arises from each of these constructions.



On the left, the colored arcs suggest the tangles filling four of the boundary components of the quotiented exterior of the MT5C. On the right, the colored arcs taken in pairs suggest the tangles descending from the Dehn surgery realization of the Dehn twists on the trefoil.

Below we plug the above tangle with three different rational tangles. Then we perform isotopies to obtain two-bridge presentations of the resulting links. In this manner we may observe how the exterior of K admits the three cyclic fillings S^3, L(18,5), and L(19,7).