Smooth spheres in IR4 with four critical points are standard.
Scharlemann, Martin
Inventiones mathematicae, Tome 82 (1985), p. 125-142 / Harvested from Göttinger Digitalisierungszentrum
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Publié le : 1985-01-01
EUDML-ID : urn:eudml:doc:143188 
@article{GDZPPN002101173,
     title = {Smooth spheres in IR4 with four critical points are standard.},
     journal = {Inventiones mathematicae},
     volume = {82},
     year = {1985},
     pages = {125-142},
     zbl = {0559.57019},
     url = {http://dml.mathdoc.fr/item/GDZPPN002101173}
}

Scharlemann, Martin. Smooth spheres in IR4 with four critical points are standard.. Inventiones mathematicae, Tome 82 (1985) pp. 125-142. http://gdmltest.u-ga.fr/item/GDZPPN002101173/