Theory Graph

chapter ‹Case Study: Single and Multi-Mutator Garbage Collection Algorithms›

section ‹Formalization of the Memory›

theory Graph imports Main begin

datatype node = Black | White

type_synonym nodes = "node list"
type_synonym edge = "nat × nat"
type_synonym edges = "edge list"

consts Roots :: "nat set"

definition Proper_Roots :: "nodes ⇒ bool" where
  "Proper_Roots M ≡ Roots≠{} ∧ Roots ⊆ {i. i<length M}"

definition Proper_Edges :: "(nodes × edges) ⇒ bool" where
  "Proper_Edges ≡ (λ(M,E). ∀i<length E. fst(E!i)<length M ∧ snd(E!i)<length M)"

definition BtoW :: "(edge × nodes) ⇒ bool" where
  "BtoW ≡ (λ(e,M). (M!fst e)=Black ∧ (M!snd e)≠Black)"

definition Blacks :: "nodes ⇒ nat set" where
  "Blacks M ≡ {i. i<length M ∧ M!i=Black}"

definition Reach :: "edges ⇒ nat set" where
  "Reach E ≡ {x. (∃path. 1<length path ∧ path!(length path - 1)∈Roots ∧ x=path!0
              ∧ (∀i<length path - 1. (∃j<length E. E!j=(path!(i+1), path!i))))
              ∨ x∈Roots}"

text‹Reach: the set of reachable nodes is the set of Roots together with the
nodes reachable from some Root by a path represented by a list of
  nodes (at least two since we traverse at least one edge), where two
consecutive nodes correspond to an edge in E.›

subsection ‹Proofs about Graphs›

lemmas Graph_defs= Blacks_def Proper_Roots_def Proper_Edges_def BtoW_def
declare Graph_defs [simp]

subsubsection‹Graph 1›

lemma Graph1_aux [rule_format]:
  "⟦ Roots⊆Blacks M; ∀i<length E. ¬BtoW(E!i,M)⟧
  ⟹ 1< length path ⟶ (path!(length path - 1))∈Roots ⟶
  (∀i<length path - 1. (∃j. j < length E ∧ E!j=(path!(Suc i), path!i)))
  ⟶ M!(path!0) = Black"
apply(induct_tac "path")
 apply force
apply clarify
apply simp
apply(case_tac "list")
 apply force
apply simp
apply(rename_tac lista)
apply(rotate_tac -2)
apply(erule_tac x = "0" in all_dupE)
apply simp
apply clarify
apply(erule allE , erule (1) notE impE)
apply simp
apply(erule mp)
apply(case_tac "lista")
 apply force
apply simp
apply(erule mp)
apply clarify
apply(erule_tac x = "Suc i" in allE)
apply force
done

lemma Graph1:
  "⟦Roots⊆Blacks M; Proper_Edges(M, E); ∀i<length E. ¬BtoW(E!i,M) ⟧
  ⟹ Reach E⊆Blacks M"
apply (unfold Reach_def)
apply simp
apply clarify
apply(erule disjE)
 apply clarify
 apply(rule conjI)
  apply(subgoal_tac "0< length path - Suc 0")
   apply(erule allE , erule (1) notE impE)
   apply force
  apply simp
 apply(rule Graph1_aux)
apply auto
done

subsubsection‹Graph 2›

lemma Ex_first_occurrence [rule_format]:
  "P (n::nat) ⟶ (∃m. P m ∧ (∀i. i<m ⟶ ¬ P i))"
apply(rule nat_less_induct)
apply clarify
apply(case_tac "∀m. m<n ⟶ ¬ P m")
apply auto
done

lemma Compl_lemma: "(n::nat)≤l ⟹ (∃m. m≤l ∧ n=l - m)"
apply(rule_tac x = "l - n" in exI)
apply arith
done

lemma Ex_last_occurrence:
  "⟦P (n::nat); n≤l⟧ ⟹ (∃m. P (l - m) ∧ (∀i. i<m ⟶ ¬P (l - i)))"
apply(drule Compl_lemma)
apply clarify
apply(erule Ex_first_occurrence)
done

lemma Graph2:
  "⟦T ∈ Reach E; R<length E⟧ ⟹ T ∈ Reach (E[R:=(fst(E!R), T)])"
apply (unfold Reach_def)
apply clarify
apply simp
apply(case_tac "∀z<length path. fst(E!R)≠path!z")
 apply(rule_tac x = "path" in exI)
 apply simp
 apply clarify
 apply(erule allE , erule (1) notE impE)
 apply clarify
 apply(rule_tac x = "j" in exI)
 apply(case_tac "j=R")
  apply(erule_tac x = "Suc i" in allE)
  apply simp
 apply (force simp add:nth_list_update)
apply simp
apply(erule exE)
apply(subgoal_tac "z ≤ length path - Suc 0")
 prefer 2 apply arith
apply(drule_tac P = "λm. m<length path ∧ fst(E!R)=path!m" in Ex_last_occurrence)
 apply assumption
apply clarify
apply simp
apply(rule_tac x = "(path!0)#(drop (length path - Suc m) path)" in exI)
apply simp
apply(case_tac "length path - (length path - Suc m)")
 apply arith
apply simp
apply(subgoal_tac "(length path - Suc m) + nat ≤ length path")
 prefer 2 apply arith
apply(subgoal_tac "length path - Suc m + nat = length path - Suc 0")
 prefer 2 apply arith
apply clarify
apply(case_tac "i")
 apply(force simp add: nth_list_update)
apply simp
apply(subgoal_tac "(length path - Suc m) + nata ≤ length path")
 prefer 2 apply arith
apply(subgoal_tac "(length path - Suc m) + (Suc nata) ≤ length path")
 prefer 2 apply arith
apply simp
apply(erule_tac x = "length path - Suc m + nata" in allE)
apply simp
apply clarify
apply(rule_tac x = "j" in exI)
apply(case_tac "R=j")
 prefer 2 apply force
apply simp
apply(drule_tac t = "path ! (length path - Suc m)" in sym)
apply simp
apply(case_tac " length path - Suc 0 < m")
 apply(subgoal_tac "(length path - Suc m)=0")
  prefer 2 apply arith
 apply(simp del: diff_is_0_eq)
 apply(subgoal_tac "Suc nata≤nat")
 prefer 2 apply arith
 apply(drule_tac n = "Suc nata" in Compl_lemma)
 apply clarify
 subgoal using [[linarith_split_limit = 0]] by force
apply(drule leI)
apply(subgoal_tac "Suc (length path - Suc m + nata)=(length path - Suc 0) - (m - Suc nata)")
 apply(erule_tac x = "m - (Suc nata)" in allE)
 apply(case_tac "m")
  apply simp
 apply simp
apply simp
done


subsubsection‹Graph 3›

declare min.absorb1 [simp] min.absorb2 [simp]

lemma Graph3:
  "⟦ T∈Reach E; R<length E ⟧ ⟹ Reach(E[R:=(fst(E!R),T)]) ⊆ Reach E"
apply (unfold Reach_def)
apply clarify
apply simp
apply(case_tac "∃i<length path - 1. (fst(E!R),T)=(path!(Suc i),path!i)")
― ‹the changed edge is part of the path›
 apply(erule exE)
 apply(drule_tac P = "λi. i<length path - 1 ∧ (fst(E!R),T)=(path!Suc i,path!i)" in Ex_first_occurrence)
 apply clarify
 apply(erule disjE)
― ‹T is NOT a root›
  apply clarify
  apply(rule_tac x = "(take m path)@patha" in exI)
  apply(subgoal_tac "¬(length path≤m)")
   prefer 2 apply arith
  apply(simp)
  apply(rule conjI)
   apply(subgoal_tac "¬(m + length patha - 1 < m)")
    prefer 2 apply arith
   apply(simp add: nth_append)
  apply(rule conjI)
   apply(case_tac "m")
    apply force
   apply(case_tac "path")
    apply force
   apply force
  apply clarify
  apply(case_tac "Suc i≤m")
   apply(erule_tac x = "i" in allE)
   apply simp
   apply clarify
   apply(rule_tac x = "j" in exI)
   apply(case_tac "Suc i<m")
    apply(simp add: nth_append)
    apply(case_tac "R=j")
     apply(simp add: nth_list_update)
     apply(case_tac "i=m")
      apply force
     apply(erule_tac x = "i" in allE)
     apply force
    apply(force simp add: nth_list_update)
   apply(simp add: nth_append)
   apply(subgoal_tac "i=m - 1")
    prefer 2 apply arith
   apply(case_tac "R=j")
    apply(erule_tac x = "m - 1" in allE)
    apply(simp add: nth_list_update)
   apply(force simp add: nth_list_update)
  apply(simp add: nth_append)
  apply(rotate_tac -4)
  apply(erule_tac x = "i - m" in allE)
  apply(subgoal_tac "Suc (i - m)=(Suc i - m)" )
    prefer 2 apply arith
   apply simp
― ‹T is a root›
 apply(case_tac "m=0")
  apply force
 apply(rule_tac x = "take (Suc m) path" in exI)
 apply(subgoal_tac "¬(length path≤Suc m)" )
  prefer 2 apply arith
 apply clarsimp
 apply(erule_tac x = "i" in allE)
 apply simp
 apply clarify
 apply(case_tac "R=j")
  apply(force simp add: nth_list_update)
 apply(force simp add: nth_list_update)
― ‹the changed edge is not part of the path›
apply(rule_tac x = "path" in exI)
apply simp
apply clarify
apply(erule_tac x = "i" in allE)
apply clarify
apply(case_tac "R=j")
 apply(erule_tac x = "i" in allE)
 apply simp
apply(force simp add: nth_list_update)
done

subsubsection‹Graph 4›

lemma Graph4:
  "⟦T ∈ Reach E; Roots⊆Blacks M; I≤length E; T<length M; R<length E;
  ∀i<I. ¬BtoW(E!i,M); R<I; M!fst(E!R)=Black; M!T≠Black⟧ ⟹
  (∃r. I≤r ∧ r<length E ∧ BtoW(E[R:=(fst(E!R),T)]!r,M))"
apply (unfold Reach_def)
apply simp
apply(erule disjE)
 prefer 2 apply force
apply clarify
― ‹there exist a black node in the path to T›
apply(case_tac "∃m<length path. M!(path!m)=Black")
 apply(erule exE)
 apply(drule_tac P = "λm. m<length path ∧ M!(path!m)=Black" in Ex_first_occurrence)
 apply clarify
 apply(case_tac "ma")
  apply force
 apply simp
 apply(case_tac "length path")
  apply force
 apply simp
 apply(erule_tac P = "λi. i < nata ⟶ P i" and x = "nat" for P in allE)
 apply simp
 apply clarify
 apply(erule_tac P = "λi. i < Suc nat ⟶ P i" and x = "nat" for P in allE)
 apply simp
 apply(case_tac "j<I")
  apply(erule_tac x = "j" in allE)
  apply force
 apply(rule_tac x = "j" in exI)
 apply(force  simp add: nth_list_update)
apply simp
apply(rotate_tac -1)
apply(erule_tac x = "length path - 1" in allE)
apply(case_tac "length path")
 apply force
apply force
done

declare min.absorb1 [simp del] min.absorb2 [simp del]

subsubsection ‹Graph 5›

lemma Graph5:
  "⟦ T ∈ Reach E ; Roots ⊆ Blacks M; ∀i<R. ¬BtoW(E!i,M); T<length M;
    R<length E; M!fst(E!R)=Black; M!snd(E!R)=Black; M!T ≠ Black⟧
   ⟹ (∃r. R<r ∧ r<length E ∧ BtoW(E[R:=(fst(E!R),T)]!r,M))"
apply (unfold Reach_def)
apply simp
apply(erule disjE)
 prefer 2 apply force
apply clarify
― ‹there exist a black node in the path to T›
apply(case_tac "∃m<length path. M!(path!m)=Black")
 apply(erule exE)
 apply(drule_tac P = "λm. m<length path ∧ M!(path!m)=Black" in Ex_first_occurrence)
 apply clarify
 apply(case_tac "ma")
  apply force
 apply simp
 apply(case_tac "length path")
  apply force
 apply simp
 apply(erule_tac P = "λi. i < nata ⟶ P i" and x = "nat" for P in allE)
 apply simp
 apply clarify
 apply(erule_tac P = "λi. i < Suc nat ⟶ P i" and x = "nat" for P in allE)
 apply simp
 apply(case_tac "j≤R")
  apply(drule le_imp_less_or_eq [of _ R])
  apply(erule disjE)
   apply(erule allE , erule (1) notE impE)
   apply force
  apply force
 apply(rule_tac x = "j" in exI)
 apply(force  simp add: nth_list_update)
apply simp
apply(rotate_tac -1)
apply(erule_tac x = "length path - 1" in allE)
apply(case_tac "length path")
 apply force
apply force
done

subsubsection ‹Other lemmas about graphs›

lemma Graph6:
 "⟦Proper_Edges(M,E); R<length E ; T<length M⟧ ⟹ Proper_Edges(M,E[R:=(fst(E!R),T)])"
apply (unfold Proper_Edges_def)
 apply(force  simp add: nth_list_update)
done

lemma Graph7:
 "⟦Proper_Edges(M,E)⟧ ⟹ Proper_Edges(M[T:=a],E)"
apply (unfold Proper_Edges_def)
apply force
done

lemma Graph8:
 "⟦Proper_Roots(M)⟧ ⟹ Proper_Roots(M[T:=a])"
apply (unfold Proper_Roots_def)
apply force
done

text‹Some specific lemmata for the verification of garbage collection algorithms.›

lemma Graph9: "j<length M ⟹ Blacks M⊆Blacks (M[j := Black])"
apply (unfold Blacks_def)
 apply(force simp add: nth_list_update)
done

lemma Graph10 [rule_format (no_asm)]: "∀i. M!i=a ⟶M[i:=a]=M"
apply(induct_tac "M")
apply auto
apply(case_tac "i")
apply auto
done

lemma Graph11 [rule_format (no_asm)]:
  "⟦ M!j≠Black;j<length M⟧ ⟹ Blacks M ⊂ Blacks (M[j := Black])"
apply (unfold Blacks_def)
apply(rule psubsetI)
 apply(force simp add: nth_list_update)
apply safe
apply(erule_tac c = "j" in equalityCE)
apply auto
done

lemma Graph12: "⟦a⊆Blacks M;j<length M⟧ ⟹ a⊆Blacks (M[j := Black])"
apply (unfold Blacks_def)
apply(force simp add: nth_list_update)
done

lemma Graph13: "⟦a⊂ Blacks M;j<length M⟧ ⟹ a ⊂ Blacks (M[j := Black])"
apply (unfold Blacks_def)
apply(erule psubset_subset_trans)
apply(force simp add: nth_list_update)
done

declare Graph_defs [simp del]

end