@article{10_4153_CMB_1974_089_x,
     author = {Etigson, L. B.},
     title = {A {Cosine} {Functional} {Equation} with {Restricted} {Argument}},
     journal = {Canadian mathematical bulletin},
     pages = {505--509},
     year = {1974},
     volume = {17},
     number = {4},
     doi = {10.4153/CMB-1974-089-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1974-089-x/}
}