  Double deeply virtual Compton scattering (DDVCS) is the process where an
electron scatters off a nucleon and produces a lepton pair. The main advantage
of this process in contrast with deeply virtual and timelike Compton
scatterings (DVCS and TCS) is the possibility of directly measuring GPDs for
$x\neq\pm\xi$ at leading order in $\alpha_s$ (LO). We present a new calculation
of the DDVCS amplitude based on the methods developed by R. Kleiss and W. J.
Stirling in the 1980s. These techniques produce expressions for amplitudes that
are perfectly suited for implementation in numerical simulations. Via the
PARTONS software, the correctness of this new formulation has been tested by
comparing the DVCS and TCS limits of DDVCS with independent calculations of
DVCS and TCS.
