@article{10_1090_S0894_0347_01_00358_7,
     author = {Hass, Joel and Lagarias, Jeffrey},
     title = {The number of {Reidemeister} moves needed for unknotting},
     journal = {Journal of the American Mathematical Society},
     pages = {399--428},
     publisher = {mathdoc},
     volume = {14},
     number = {2},
     year = {2001},
     doi = {10.1090/S0894-0347-01-00358-7},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-01-00358-7/}
}