@article{10_5427_jsing_2015_12o,
     author = {Yongqiao Wang and Donghe Pei},
     title = {Singularities for normal hypersurfaces of de {Sitter} timelike curves in {Minkowski} 4-space},
     journal = {Journal of Singularities},
     pages = {207--214},
     publisher = {mathdoc},
     volume = {12},
     year = {2015},
     doi = {10.5427/jsing.2015.12o},
     url = {http://geodesic.mathdoc.fr/articles/10.5427/jsing.2015.12o/}
}