(* Title: HOL/UNITY/Constrains
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1998 University of Cambridge
Safety relations: restricted to the set of reachable states.
*)
Constrains = UNITY + Traces +
constdefs
Constrains :: "['a program, 'a set, 'a set] => bool"
"Constrains prg A B ==
constrains (Acts prg)
(reachable prg Int A)
(reachable prg Int B)"
Stable :: "'a program => 'a set => bool"
"Stable prg A == Constrains prg A A"
Unless :: "['a program, 'a set, 'a set] => bool"
"Unless prg A B == Constrains prg (A-B) (A Un B)"
Invariant :: "['a program, 'a set] => bool"
"Invariant prg A == (Init prg) <= A & Stable prg A"
end