We classify Dehn surgeries on .p; q; r / pretzel knots that result in a manifold of finite fundamental group. The only hyperbolic pretzel knots that admit nontrivial finite surgeries are . 2; 3; 7/ and . 2; 3; 9/. Agol and Lackenby's 6-theorem reduces the argument to knots with small indices p; q; r . We treat these using the Culler-Shalen norm of the SL.2; C/-character variety. In particular, we introduce new techniques for demonstrating that boundary slopes are detected by the character variety.
57M05, 57M25, 57M50Dedicated to Professor Akio Kawauchi on the occasion of his 60th birthday.In [19] Mattman showed that if a hyperbolic .p; q; r / pretzel knot K admits a nontrivial finite Dehn surgery of slope s (ie, a Dehn surgery that results in a manifold of finite fundamental group) then either K D . 2; 3; 7/ and s D 17, 18 or 19, K D . 2; 3; 9/ and s D 22 or 23 or K D . 2; p; q/ where p and q are odd and 5 Ä p Ä q .In the current paper we complete the classification by proving:Theorem 1 Let K be a . 2; p; q/ pretzel knot with p , q odd and 5 Ä p Ä q . Then K admits no nontrivial finite surgery.Using the work of Agol [1] and Lackenby [16], candidates for finite surgery correspond to curves of length at most six in the maximal cusp of S 3 n K . If 7 Ä p Ä q , we will argue that only five slopes for the . 2; p; q/ pretzel knot have length six or less: the meridian and the four integral surgeries 2.p C q/ 1, 2.p C q/, 2.p C q/ C 1 and 2.p C q/ C 2. If p D 5 and q 11, a similar argument leaves seven candidates, the meridian and the six integral slopes between 2.5 C q/ 2 and 2.5 C q/ C 3.