On the Formation of Quantum-Mechanical Operators, John Robert Shewell, Am. J. Phys, 27, 1959
A number of rules for forming operators corresponding to classical quantities are investigated. Spin and relativistic are excluded from consideration. The two rules which are in agreement with customary interpretation of quantum mechanics are ambiguous in that they do not yield unique operators. The other rules considered yield unique operators but are in disagreement with the customary interpretation of quantum mechanics. It is shown that any symmetrtization rule is in this category. All the rules investigated are linear, but no attempt is made to formulate a nonlinear rule. It is indicated that additional experimental evidence is needed.