A new approach, using simp_of_act and simp_of_set to activate definitions when
necessary
(* 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