The set of observables of a Quantum Mechanical System need only be closed under a "quadratic" product. It is shown that an additive structure of this set (whose existence is less natural) is uniquely determined by this multiplicative structure.
Cite this article
Yaakov Friedman, Josuke Hakeda, Additivity of Quadratic Maps. Publ. Res. Inst. Math. Sci. 24 (1988), no. 5, pp. 707–722DOI 10.2977/PRIMS/1195174689