@article{AM2_1984__27_137021,
     author = {Harshinder Singh and H.L. Vasudeva},
     title = {Exponential-cosine operator-valued functional equation in the strong operator topology.},
     journal = {Aequationes mathematicae},
     pages = {187--197},
     publisher = {mathdoc},
     volume = {27},
     year = {1984},
     zbl = {0558.47032},
     url = {http://geodesic.mathdoc.fr/item/AM2_1984__27_137021/}
}