@article{10_4171_ifb_334,
     author = {Cong Qin and Xinfu Chen and Xin Lai and Wanghui Yu},
     title = {Regularity of free boundary arising from optimal exercise of perpetual executive stock options},
     journal = {Interfaces and free boundaries},
     pages = {69--92},
     year = {2015},
     volume = {17},
     number = {1},
     doi = {10.4171/ifb/334},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ifb/334/}
}