Theory TimerArray (Isabelle2005: October 2005)

# Theory TimerArray

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theory TimerArray
imports UNITY_Main
begin

    (*  Title:      HOL/UNITY/TimerArray.thy
        ID:         $Id: TimerArray.thy,v 1.5 2005/06/17 14:13:10 haftmann Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1998  University of Cambridge

    A trivial example of reasoning about an array of processes
    *)

    theory TimerArray imports UNITY_Main begin

    types 'a state = "nat * 'a"   (*second component allows new variables*)

    constdefs
      count  :: "'a state => nat"
        "count s == fst s"

      decr  :: "('a state * 'a state) set"
        "decr == UN n uu. {((Suc n, uu), (n,uu))}"

      Timer :: "'a state program"
        "Timer == mk_total_program (UNIV, {decr}, UNIV)"

    declare Timer_def [THEN def_prg_Init, simp]

    declare count_def [simp] decr_def [simp]

    (*Demonstrates induction, but not used in the following proof*)
    lemma Timer_leadsTo_zero: "Timer : UNIV leadsTo {s. count s = 0}"
    apply (rule_tac f = count in lessThan_induct, simp)
    apply (case_tac "m")
     apply (force intro!: subset_imp_leadsTo)
    apply (unfold Timer_def, ensures_tac "decr")
    done

    lemma Timer_preserves_snd [iff]: "Timer : preserves snd"
    apply (rule preservesI)
    apply (unfold Timer_def, safety)
    done

    declare PLam_stable [simp]

    lemma TimerArray_leadsTo_zero:
         "finite I
          ==> (plam i: I. Timer) : UNIV leadsTo {(s,uu). ALL i:I. s i = 0}"
    apply (erule_tac A'1 = "%i. lift_set i ({0} <*> UNIV)"
           in finite_stable_completion [THEN leadsTo_weaken])
    apply auto
    (*Safety property, already reduced to the single Timer case*)
     prefer 2
     apply (simp add: Timer_def, safety)
    (*Progress property for the array of Timers*)
    apply (rule_tac f = "sub i o fst" in lessThan_induct)
    apply (case_tac "m")
    (*Annoying need to massage the conditions to have the form (... <*> UNIV)*)
    apply (auto intro: subset_imp_leadsTo
            simp add: insert_absorb
                      lift_set_Un_distrib [symmetric] lessThan_Suc [symmetric]
                   Times_Un_distrib1 [symmetric] Times_Diff_distrib1 [symmetric])
    apply (rename_tac "n")
    apply (rule PLam_leadsTo_Basis)
    apply (auto simp add: lessThan_Suc [symmetric])
    apply (unfold Timer_def mk_total_program_def, safety)
    apply (rule_tac act = decr in totalize_transientI, auto)
    done

    end

lemma Timer_leadsTo_zero:

      Timer ∈ UNIV leadsTo {s. TimerArray.count s = 0}

lemma Timer_preserves_snd:

      Timer ∈ preserves snd

lemma TimerArray_leadsTo_zero:

      finite I ==> (plam i:I. Timer) ∈ UNIV leadsTo {(s, uu). ∀i∈I. s i = 0}