@article {2001, title = {Morse properties for the minimum time function on 2-D manifolds}, journal = {J. Dynam. Control Systems 7 (2001), no. 3, 385--423}, number = {SISSA;84/00/M}, year = {2001}, publisher = {SISSA Library}, doi = {10.1023/A:1013190914234}, url = {http://hdl.handle.net/1963/1541}, author = {Ugo Boscain and Benedetto Piccoli} }