Proof methods.
(* Title: HOL/lfp.thy
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1992 University of Cambridge
The Knaster-Tarski Theorem
*)
Lfp = Set +
consts lfp :: "['a set=>'a set] => 'a set"
rules
(*least fixed point*)
lfp_def "lfp(f) == Inter({u. f(u) <= u})"
end