@article{10_4153_CMB_1968_059_8,
     author = {Kannappan, PL},
     title = {A {Functional} {Equation} for the {Cosine}},
     journal = {Canadian mathematical bulletin},
     pages = {495--498},
     year = {1968},
     volume = {11},
     number = {3},
     doi = {10.4153/CMB-1968-059-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1968-059-8/}
}