  The collision between a positronium (Ps) and a muonium (Mu) is studied for
the first time using the static-exchange model and considering the system as a
four-center Coulomb problem in the center of mass frame. An exact analysis is
made to find the s-wave elastic phase-shifts, the scattering-lengths for both
singlet and triplet channels, the integrated/total elastic cross section and
the quenching cross section due to ortho to para conversion of Ps and the
conversion ratio.
