  A method for the extraction of an effective meson-meson potential from Green
functions, which can be obtained from a lattice simulation, is presented.
Simulations are carried out for compact QED and QCD in four dimensions using
the quenched approximation and the hopping parameter expansion. In a further
study, a heavy-light meson is considered employing a conjugate gradient
algorithm for the light propagators. Due to the Pauli exclusion principle, the
results for QED indicate the existence of a hard core, but for QCD there is
strong attraction at small meson distances.
