@article{IM_1985__79_143188,
     author = {Martin Scharlemann},
     title = {Smooth spheres in {IR4} with four critical points are standard.},
     journal = {Inventiones mathematicae},
     pages = {125--142},
     year = {1985},
     volume = {79},
     zbl = {0559.57019},
     url = {http://geodesic.mathdoc.fr/item/IM_1985__79_143188/}
}