@article{SF_1986__34_134849,
     author = {J.A. Goldstein and S. \^Oharu},
     title = {A remark on nonlinear cosine functions.},
     journal = {Semigroup forum},
     pages = {359--366},
     publisher = {mathdoc},
     volume = {34},
     year = {1986},
     zbl = {0609.47075},
     url = {http://geodesic.mathdoc.fr/item/SF_1986__34_134849/}
}