@article{10_4064_sm_42_1_43_66,
     author = {J. Kisy\'nski},
     title = {On operator valued solutions of {d'Alembert's} functional equation, {II}},
     journal = {Studia Mathematica},
     pages = {43--66},
     publisher = {mathdoc},
     volume = {42},
     number = {1},
     year = {1972},
     doi = {10.4064/sm-42-1-43-66},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-42-1-43-66/}
}