Now Datatype.occs_in_prems prints the necessary warning ITSELF.
It is also easier to invoke and even works if the induction variable
is a parameter (rather than a free variable).
(* 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 +
consts
theleast :: "(nat=>bool)=>nat"
rules
theleast_def "theleast(P) == (@z.(P(z) & (!n.P(n)-->z<=n)))"
end