In a recent thread with Justo, I mentioned this problem but only in passing. Here I want to highlight it because, by itself, it shows Bell's faulty logic right from his original paper. I don't know if anyone has described this problem before and I have not come across any attempt in Bell's other papers to address the problem. In any case, the fact that such a clear error exists in Bell's original paper should be a red flag for anyone who takes him seriously. Now unto the argument.
In his paper, Bell is dealing with correlations between pairs of particles formed in the singlet state and moving in opposite directions towards measurement stations and those correlations are specified as the average of the paired product of outcomes observed at those stations
)
.
Note that
)
is the correlation between pairs of particles in the singlet state. According to QM,
 = -a \cdot b)
, and
 = -a \cdot c)
and obviously
 = -b \cdot c)
. This is not controversial at all and perfectly above board.
But this is where Bell makes the mistake. He derives his inequality by starting with the expression:
 - P(a,c))
Note that here we have two series of particles in the singlet state. The first series measured at
)
and the second measured at
)
. Obviously, the QM prediction for this expression is
 - P(a,c) = - a \cdot b + a \cdot c)
. However, Bell then makes a massive blunder! He uses some arithmetic operations from equations 14a to 15 which effectively amount to calculating the correlation between one member of the singlet pairs used to obtain
)
and one member of the distinct set of singlet pairs used to obtain
)
. This is obvious from his calculations. the
)
appearing in equation (15), is not simply another measurement performed on yet a different distinct series of particle pairs in the singlet state which should have a QM prediction of
 = -b \cdot c)
. Rather
)
in Bell's equation (15) is a "franken-correlation", reassembled using parts of
)
and parts of
)
as is obvious from the arithmetic preceding equation 15. For that reason, let us identify it as
)
.
In other words,
)
is the correlation you would expect between one member of a singlet pair and one member of a different singlet pair. Yet, in equation (22), Bell uses the same QM prediction
 = P(b,c) = -b \cdot c)
, that would be expected for a distinct set of particle pairs in the singlet state.
It turns out QM has something to say about Bell's "franken-correlation"
)
. According to QM,
 = 0)
.
Using the correct QM prediction for
 = 0)
. Bell's theorem can't be derived. Specifically, the proof of the contradiction fails and there is no "violation" by QM.