  We consider a scalar wave propagation in harmonic regime modelled by
Helmholtz equation with heterogeneous coefficients. Using the Multi-Trace
Formalism (MTF), we propose a new variant of the Optimized Schwarz Method (OSM)
that can accomodate the presence of cross-points in the subdomain partition.
This leads to the derivation of a strongly coercive formulation of our
Helmholtz problem posed on the union of all interfaces. The corresponding
operator takes the form "identity + contraction".
