  The differential cross section and analyzing power $A_y$ of the ${\vec
p}p{\to}pp{\pi}^0$ reaction have been measured at RCNP in coplanar geometry at
a beam energy of 390 MeV and the dependence on both the pion emission angle and
the relative momentum of the final protons have been extracted. The angular
variation of Ay for the large values of the relative momentum studied here
shows that this is primarily an effect of the interference of pion s- and
p-waves and this interference can also explain the momentum dependence. Within
the framework of a very simple model, these results would suggest that the
pion-production operator has a significant long-range component.
