@article{AM2_1986__31_137147,
     author = {R.R. Kocherlakota},
     title = {Functions of a quaternion variable which are gradients of real-valued functions.},
     journal = {Aequationes mathematicae},
     pages = {109--117},
     publisher = {mathdoc},
     volume = {31},
     year = {1986},
     zbl = {0603.30058},
     url = {http://geodesic.mathdoc.fr/item/AM2_1986__31_137147/}
}