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**Joel Hass** is an American mathematician and a professor of mathematics and at the University of California, Davis.^{[1]} His work focuses on geometric and topological problems in dimension 3.

Hass received his Ph.D. from the University of California, Berkeley in 1981 under the supervision of Robion Kirby.^{[2]} He joined the Davis faculty in 1988.^{[1]}

In 2012 he became a fellow of the American Mathematical Society.^{[3]} From 2010 to 2014 he served as the chair of the UC Davis mathematics department.^{[4]}

Hass is known for proving the equal-volume special case of the double bubble conjecture,^{[5]} for proving that the unknotting problem is in NP,^{[6]} and for giving an exponential bound on the number of Reidemeister moves needed to reduce the unknot to a circle.^{[7]}

- Research papers

- Freedman, Michael; Hass, Joel; Scott, Peter (1983), "Least area incompressible surfaces in 3-manifolds" (PDF),
*Inventiones Mathematicae*,**71**(3): 609–642, Bibcode:1983InMat..71..609F, doi:10.1007/BF02095997, hdl:2027.42/46610, MR 0695910, S2CID 42502819. - Hass, Joel; Lagarias, Jeffrey C.; Pippenger, Nicholas (1999), "The computational complexity of knot and link problems",
*Journal of the ACM*,**46**(2): 185–211, arXiv:math/9807016, doi:10.1145/301970.301971, S2CID 125854. - Hass, Joel; Schlafly, Roger (2000), "Double bubbles minimize",
*Annals of Mathematics*, Second Series,**151**(2): 459–515, arXiv:math/0003157, Bibcode:2000math......3157H, doi:10.2307/121042, JSTOR 121042, MR 1765704, S2CID 15663910. - Hass, Joel; Lagarias, Jeffrey C. (2001), "The number of Reidemeister moves needed for unknotting",
*Journal of the American Mathematical Society*,**14**(2): 399–428, arXiv:math/9807012, doi:10.1090/S0894-0347-01-00358-7, MR 1815217, S2CID 15654705.

- Books

- Adams, Colin; Hass, Joel; Thompson, Abigail (1998),
*How to Ace Calculus: The Streetwise Guide*, New York: W.H. Freeman and Company, ISBN 0-7167-3160-6. - Adams, Colin; Hass, Joel; Thompson, Abigail (2001),
*How to Ace the Rest of Calculus: The Streetwise Guide*, New York: W.H. Freeman and Company, ISBN 0-7167-4174-1.

2004: Student Solutions Manual, Maurice D. Weir, Joel Hass, George B. Thomas, Frank R Giordano

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^{a}^{b}Faculty profile and math department contact information, UC Davis, retrieved 2012-07-03. **^**Joel Hass at the Mathematics Genealogy Project**^**List of Fellows of the American Mathematical Society, retrieved 2013-01-19.**^**"Editorial and other Service".*www.math.ucdavis.edu*. Retrieved 2021-11-16.**^**Hass & Schlafly (2000).**^**Hass, Lagarias & Pippenger (1999).**^**Hass & Lagarias (2001).

- Home page at UC Davis
- Google scholar profile