how to interpret negative probabilities but how to employ them.

Not everybody thinks that the idea of negative probabilities is a good one. Let’s hear a critic. In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen surmised that quantum mechanics is incomplete, i.e., that some hidden variables are missing [@EPR]. John Bell proved that local hidden-variable theories contradict quantum-mechanical statistics [@Bell]. It seems natural to try to save the hidden-variable approach by means of negative probabilities, and here is what our critic, Itamar Pitowsky, has to say about that [@Pitowsky page 148].

> What makes the classical hidden variable theories “classical” is the identification of “mixtures of hidden variable states” as probability measures…The logical step to take …is …to use (cheap) tricks such as negative “probability”, or even complex “probability” values. Formally we may be able to “solve” our problem, but then the term “probability” loses completely its meaning. …It is absurd to talk about an urn containing $-17$ red balls or $3e^{i\pi/12}$ wooden balls.

We wrote about negative probabilities once [@G224]. Here we wish to defend the cheap trick of negative probabilities. Indeed, the standard frequential interpretation of probabilities does not apply to negative probabilities. But here is an 