  The correlation factor for diffusion by the divacancy mechanism in an FCC
lattice has been the target of a long quest. Amounting to 0.54 at the
beginning, its value was progressively decreased down to 0.4582 with a
confidence interval of 0.0005. The limitations of previous studies came from
the matrix method at work which confined the defect trajectories to a volume of
finite extension around the tracer atom, or, more basically, from the
availability of computing time for the numerical simulations. The present study
determines the exact value thanks to a double Laplace-Fourier transform of the
transport equation, which takes into account all the divacancy trajectories
without any limitation of their lengths. The exact value is lower than all the
preceding evaluations, but falls within the confidence interval which was
estimated from the best evaluations based on simulations. One interesting
byproduct of our analytical approach is the proof of the equality t11=t22.
