Put in minimal simpset to avoid excessive simplification,
just as in revision 1.9 of HOL/indrule.ML
(* Title: HOLCF/holcfb.thy
ID: $Id$
Author: Franz Regensburger
Copyright 1993 Technische Universitaet Muenchen
Basic definitions for the embedding of LCF into HOL.
*)
Holcfb = Nat