[[1] Baron K., Rätz J., On orthogonally additive mappings on inner product spaces, Bull. Polish Acad. Sci. Math. 43 (1995), 187–189.]Search in Google Scholar
[[2] Kuczma M., An introduction to the theory of functional equations and inequalities. Cauchy’s equation and Jensen’s inequality, Second edition (edited by A. Gilányi), Birkhäuser Verlag, Basel, 2009.10.1007/978-3-7643-8749-5]Search in Google Scholar
[[3] Rätz J., On orthogonally additive mappings, Aequationes Math. 28 (1985), 35–49.10.1007/BF02189390]Search in Google Scholar
[[4] Sikorska J., Orthogonalities and functional equations, Aequationes Math. 89 (2015), 215–277.10.1007/s00010-014-0288-0]Search in Google Scholar