  Proton-antiproton annihilation into two pions and three pions is studied in a
baryon-exchange model. Annihilation diagrams involving nucleon as well as
Delta-resonance exchanges are included consistently in the two- and three-pion
channels. Effects from the initial-state interaction are fully taken into
account. A comparison of the influence of the Delta exchange on the considered
annihilation channels is made and reveals that its importance for three-pion
annihilation is strongly reduced as compared to two-pion annihilation. It is
found that annihilation into three uncorrelated pions can yield up to 10 % of
the total experimentally observed three-pion annihilation cross section.
