  We show that the definition of unipotent (resp. nilpotent) pieces for
classical groups given by Lusztig (resp. Lusztig and the author) coincides with
the combinatorial definition using closure relations on unipotent classes
(resp. nilpotent orbits). Moreover we give a closed formula for a map from the
set of unipotent classes (resp. nilpotent orbits) in characteristic 2 to the
set of unipotent classes in characteristic 0 such that the fibers are the
unipotent (resp. nilpotent) pieces.
