  We refined the crystal structure of AMnO3, with A = Y, Er, Yb and Lu by
single crystal x-ray diffraction. Our results show some distinct differences
with previous reports on LuMnO3 and YbMnO3. We show that the ferroelectric
behaviour is originated in the dipole moment at the A-site, and not, as is the
common opinion, at the Mn site.
