  Let K be a complete discretely valued field of mixed characteristic (0, p)
with possibly imperfect residue field. We prove a Hasse-Arf theorem for the
arithmetic ramification filtrations on G_K, except possibly in the absolutely
unramified and non-logarithmic case, or p=2 and logarithmic case. As an
application, we obtain a Hasse-Arf theorem for filtrations on finite flat group
schemes over O_K.
