got rid of split_diff, which duplicated nat_diff_split, and
also disposed of remove_diff_ss
(* Title: HOLCF/ssum2.thy
ID: $Id$
Author: Franz Regensburger
Copyright 1993 Technische Universitaet Muenchen
Class Instance ++::(pcpo,pcpo)po
*)
Ssum2 = Ssum1 +
instance "++"::(pcpo,pcpo)po (refl_less_ssum,antisym_less_ssum,trans_less_ssum)
end