@article{AM2_1975__12_136498,
     author = {A.B. Buche},
     title = {On an {Exponential-Cosine} {Operator-Valued} {Functional} {Equation.} {(Short} {Communication).}},
     journal = {Aequationes mathematicae},
     pages = {117--117},
     publisher = {mathdoc},
     volume = {12},
     year = {1975},
     zbl = {0334.39002},
     url = {http://geodesic.mathdoc.fr/item/AM2_1975__12_136498/}
}