  We report on an exact calculation of lattice correlation functions on a
finite four-dimensional lattice with either Euclidean or Minkowskian signature.
The lattice correlation functions are calculated by the method of differential
equations. This method can be used for Euclidean and Minkowskian signature
alike. The lattice correlation functions have a power series expansion in
$1/\sqrt{\lambda}$, where $\lambda$ is the coupling. We show that this series
is convergent for all non-zero values of $\lambda$. At small coupling we
quantify the accuracy of perturbative approximations. At the technical level we
systematically investigate the interplay between twisted cohomology and the
symmetries of the twist function.
