  This, however, is impossible, in general. An example very easily shows how (3) is violated, but because of its simplicity it also shows the argument’s inadequacy. (This example is not due to von Neumann himself, but to  Bell![3])   Let A = σx and B = σy, then operator C = (σx + σy)/√2 corresponds to the observable of the spin component along the direction bisecting x and y. Now all spin components have (in suitable units) possible values ±1 only, thus, the HV proponent is forced to ascribe ±1 to A, B, C as values, and thus as ‘expectation values’. But (3) now obviously cannot be fulfilled, since ±1 ≠ (±1 + ±1)/√2.