# Joel Hass

**Joel Hass** is an American mathematician, a professor of mathematics and chair of the mathematics department at the University of California, Davis.[1]

## Biography

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]

## Research contributions

Hass is known for proving the equal-volume special case of the double bubble conjecture,[4] for proving that the unknotting problem is in NP,[5] and for giving an exponential bound on the number of Reidemeister moves needed to reduce the unknot to a circle.[6]

## Selected publications

- 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, MR 0695910. - 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. - Hass, Joel; Schlafly, Roger (2000), "Double bubbles minimize",
*Annals of Mathematics*, Second Series,**151**(2): 459–515, arXiv:math/0003157, doi:10.2307/121042, MR 1765704. - 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.

- 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.

## References

- 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.
- Hass & Schlafly (2000).
- Hass, Lagarias & Pippenger (1999).
- Hass & Lagarias (2001).

## External links

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