suffer from the same problem that the claimed probability cannot be written as the expectation of a quantum proposition, i.e., a projector. For example, in his 1976 lecture notes on the ‘interpretation of quantum mechanics’, [Wigner]{} [@Wig p.288] writes,

[*\[...\] it remains essentially correct to say that the basic statement of quantum mechanics can be given in a formula as simple as .* ]{}

In adapted notation, for a finite sequence $a,b,c,d\dots$ of results of measurements of $A,B,C,D,\dots$, it reads

[ll]{} P\_[abcd...]{}&=\_a\_b\_c\_d \_d\_c\_b / \_a\
&=a|\_b\_c\_d \_d\_c\_b|a    

Now there is a problem with . It implies that repeating the measurement of $A$ immediately after a first measurement of $A$ gives the result of the first measurement with certainty. This is possible only if we assume that the measurements performed are ideal.

But (cf. Wigner’s discussion in pp.283-284 of [@Wig]; see also [@JooZ]) one cannot make an ideal measurement of an observable with a continuous spectrum; and the quantum mechanical analysis of the measurement process shows that an ideal measurement of any quantity takes, strictly speaking, an infinite time. And even allowing for that, the only measurable observables would be the functions of scattering invariants (p.298). Hence formula can apply to 