--- a/Myhill.thy Thu Feb 03 09:54:19 2011 +0000
+++ b/Myhill.thy Thu Feb 03 12:00:06 2011 +0000
@@ -1,900 +1,11 @@
theory Myhill
- imports Myhill_1
+ imports Myhill_2
begin
section {* Direction @{text "regular language \<Rightarrow>finite partition"} *}
-subsection {* The scheme*}
-
-text {*
- The following convenient notation @{text "x \<approx>Lang y"} means:
- string @{text "x"} and @{text "y"} are equivalent with respect to
- language @{text "Lang"}.
- *}
-
-definition
- str_eq :: "string \<Rightarrow> lang \<Rightarrow> string \<Rightarrow> bool" ("_ \<approx>_ _")
-where
- "x \<approx>Lang y \<equiv> (x, y) \<in> (\<approx>Lang)"
-
text {*
- The main lemma (@{text "rexp_imp_finite"}) is proved by a structural induction over regular expressions.
- While base cases (cases for @{const "NULL"}, @{const "EMPTY"}, @{const "CHAR"}) are quite straight forward,
- the inductive cases are rather involved. What we have when starting to prove these inductive caes is that
- the partitions induced by the componet language are finite. The basic idea to show the finiteness of the
- partition induced by the composite language is to attach a tag @{text "tag(x)"} to every string
- @{text "x"}. The tags are made of equivalent classes from the component partitions. Let @{text "tag"}
- be the tagging function and @{text "Lang"} be the composite language, it can be proved that
- if strings with the same tag are equivalent with respect to @{text "Lang"}, expressed as:
- \[
- @{text "tag(x) = tag(y) \<Longrightarrow> x \<approx>Lang y"}
- \]
- then the partition induced by @{text "Lang"} must be finite. There are two arguments for this.
- The first goes as the following:
- \begin{enumerate}
- \item First, the tagging function @{text "tag"} induces an equivalent relation @{text "(=tag=)"}
- (defiintion of @{text "f_eq_rel"} and lemma @{text "equiv_f_eq_rel"}).
- \item It is shown that: if the range of @{text "tag"} (denoted @{text "range(tag)"}) is finite,
- the partition given rise by @{text "(=tag=)"} is finite (lemma @{text "finite_eq_f_rel"}).
- Since tags are made from equivalent classes from component partitions, and the inductive
- hypothesis ensures the finiteness of these partitions, it is not difficult to prove
- the finiteness of @{text "range(tag)"}.
- \item It is proved that if equivalent relation @{text "R1"} is more refined than @{text "R2"}
- (expressed as @{text "R1 \<subseteq> R2"}),
- and the partition induced by @{text "R1"} is finite, then the partition induced by @{text "R2"}
- is finite as well (lemma @{text "refined_partition_finite"}).
- \item The injectivity assumption @{text "tag(x) = tag(y) \<Longrightarrow> x \<approx>Lang y"} implies that
- @{text "(=tag=)"} is more refined than @{text "(\<approx>Lang)"}.
- \item Combining the points above, we have: the partition induced by language @{text "Lang"}
- is finite (lemma @{text "tag_finite_imageD"}).
- \end{enumerate}
-*}
-
-definition
- f_eq_rel ("=_=")
-where
- "(=f=) = {(x, y) | x y. f x = f y}"
-
-lemma equiv_f_eq_rel:"equiv UNIV (=f=)"
- by (auto simp:equiv_def f_eq_rel_def refl_on_def sym_def trans_def)
-
-lemma finite_range_image: "finite (range f) \<Longrightarrow> finite (f ` A)"
- by (rule_tac B = "{y. \<exists>x. y = f x}" in finite_subset, auto simp:image_def)
-
-lemma finite_eq_f_rel:
- assumes rng_fnt: "finite (range tag)"
- shows "finite (UNIV // (=tag=))"
-proof -
- let "?f" = "op ` tag" and ?A = "(UNIV // (=tag=))"
- show ?thesis
- proof (rule_tac f = "?f" and A = ?A in finite_imageD)
- -- {*
- The finiteness of @{text "f"}-image is a simple consequence of assumption @{text "rng_fnt"}:
- *}
- show "finite (?f ` ?A)"
- proof -
- have "\<forall> X. ?f X \<in> (Pow (range tag))" by (auto simp:image_def Pow_def)
- moreover from rng_fnt have "finite (Pow (range tag))" by simp
- ultimately have "finite (range ?f)"
- by (auto simp only:image_def intro:finite_subset)
- from finite_range_image [OF this] show ?thesis .
- qed
- next
- -- {*
- The injectivity of @{text "f"}-image is a consequence of the definition of @{text "(=tag=)"}:
- *}
- show "inj_on ?f ?A"
- proof-
- { fix X Y
- assume X_in: "X \<in> ?A"
- and Y_in: "Y \<in> ?A"
- and tag_eq: "?f X = ?f Y"
- have "X = Y"
- proof -
- from X_in Y_in tag_eq
- obtain x y
- where x_in: "x \<in> X" and y_in: "y \<in> Y" and eq_tg: "tag x = tag y"
- unfolding quotient_def Image_def str_eq_rel_def
- str_eq_def image_def f_eq_rel_def
- apply simp by blast
- with X_in Y_in show ?thesis
- by (auto simp:quotient_def str_eq_rel_def str_eq_def f_eq_rel_def)
- qed
- } thus ?thesis unfolding inj_on_def by auto
- qed
- qed
-qed
-
-lemma finite_image_finite: "\<lbrakk>\<forall> x \<in> A. f x \<in> B; finite B\<rbrakk> \<Longrightarrow> finite (f ` A)"
- by (rule finite_subset [of _ B], auto)
-
-lemma refined_partition_finite:
- fixes R1 R2 A
- assumes fnt: "finite (A // R1)"
- and refined: "R1 \<subseteq> R2"
- and eq1: "equiv A R1" and eq2: "equiv A R2"
- shows "finite (A // R2)"
-proof -
- let ?f = "\<lambda> X. {R1 `` {x} | x. x \<in> X}"
- and ?A = "(A // R2)" and ?B = "(A // R1)"
- show ?thesis
- proof(rule_tac f = ?f and A = ?A in finite_imageD)
- show "finite (?f ` ?A)"
- proof(rule finite_subset [of _ "Pow ?B"])
- from fnt show "finite (Pow (A // R1))" by simp
- next
- from eq2
- show " ?f ` A // R2 \<subseteq> Pow ?B"
- unfolding image_def Pow_def quotient_def
- apply auto
- by (rule_tac x = xb in bexI, simp,
- unfold equiv_def sym_def refl_on_def, blast)
- qed
- next
- show "inj_on ?f ?A"
- proof -
- { fix X Y
- assume X_in: "X \<in> ?A" and Y_in: "Y \<in> ?A"
- and eq_f: "?f X = ?f Y" (is "?L = ?R")
- have "X = Y" using X_in
- proof(rule quotientE)
- fix x
- assume "X = R2 `` {x}" and "x \<in> A" with eq2
- have x_in: "x \<in> X"
- unfolding equiv_def quotient_def refl_on_def by auto
- with eq_f have "R1 `` {x} \<in> ?R" by auto
- then obtain y where
- y_in: "y \<in> Y" and eq_r: "R1 `` {x} = R1 ``{y}" by auto
- have "(x, y) \<in> R1"
- proof -
- from x_in X_in y_in Y_in eq2
- have "x \<in> A" and "y \<in> A"
- unfolding equiv_def quotient_def refl_on_def by auto
- from eq_equiv_class_iff [OF eq1 this] and eq_r
- show ?thesis by simp
- qed
- with refined have xy_r2: "(x, y) \<in> R2" by auto
- from quotient_eqI [OF eq2 X_in Y_in x_in y_in this]
- show ?thesis .
- qed
- } thus ?thesis by (auto simp:inj_on_def)
- qed
- qed
-qed
-
-lemma equiv_lang_eq: "equiv UNIV (\<approx>Lang)"
- unfolding equiv_def str_eq_rel_def sym_def refl_on_def trans_def
- by blast
-
-lemma tag_finite_imageD:
- fixes tag
- assumes rng_fnt: "finite (range tag)"
- -- {* Suppose the rang of tagging fucntion @{text "tag"} is finite. *}
- and same_tag_eqvt: "\<And> m n. tag m = tag (n::string) \<Longrightarrow> m \<approx>Lang n"
- -- {* And strings with same tag are equivalent *}
- shows "finite (UNIV // (\<approx>Lang))"
-proof -
- let ?R1 = "(=tag=)"
- show ?thesis
- proof(rule_tac refined_partition_finite [of _ ?R1])
- from finite_eq_f_rel [OF rng_fnt]
- show "finite (UNIV // =tag=)" .
- next
- from same_tag_eqvt
- show "(=tag=) \<subseteq> (\<approx>Lang)"
- by (auto simp:f_eq_rel_def str_eq_def)
- next
- from equiv_f_eq_rel
- show "equiv UNIV (=tag=)" by blast
- next
- from equiv_lang_eq
- show "equiv UNIV (\<approx>Lang)" by blast
- qed
-qed
-
-text {*
- A more concise, but less intelligible argument for @{text "tag_finite_imageD"}
- is given as the following. The basic idea is still using standard library
- lemma @{thm [source] "finite_imageD"}:
- \[
- @{thm "finite_imageD" [no_vars]}
- \]
- which says: if the image of injective function @{text "f"} over set @{text "A"} is
- finite, then @{text "A"} must be finte, as we did in the lemmas above.
- *}
-
-lemma
- fixes tag
- assumes rng_fnt: "finite (range tag)"
- -- {* Suppose the rang of tagging fucntion @{text "tag"} is finite. *}
- and same_tag_eqvt: "\<And> m n. tag m = tag (n::string) \<Longrightarrow> m \<approx>Lang n"
- -- {* And strings with same tag are equivalent *}
- shows "finite (UNIV // (\<approx>Lang))"
- -- {* Then the partition generated by @{text "(\<approx>Lang)"} is finite. *}
-proof -
- -- {* The particular @{text "f"} and @{text "A"} used in @{thm [source] "finite_imageD"} are:*}
- let "?f" = "op ` tag" and ?A = "(UNIV // \<approx>Lang)"
- show ?thesis
- proof (rule_tac f = "?f" and A = ?A in finite_imageD)
- -- {*
- The finiteness of @{text "f"}-image is a simple consequence of assumption @{text "rng_fnt"}:
- *}
- show "finite (?f ` ?A)"
- proof -
- have "\<forall> X. ?f X \<in> (Pow (range tag))" by (auto simp:image_def Pow_def)
- moreover from rng_fnt have "finite (Pow (range tag))" by simp
- ultimately have "finite (range ?f)"
- by (auto simp only:image_def intro:finite_subset)
- from finite_range_image [OF this] show ?thesis .
- qed
- next
- -- {*
- The injectivity of @{text "f"} is the consequence of assumption @{text "same_tag_eqvt"}:
- *}
- show "inj_on ?f ?A"
- proof-
- { fix X Y
- assume X_in: "X \<in> ?A"
- and Y_in: "Y \<in> ?A"
- and tag_eq: "?f X = ?f Y"
- have "X = Y"
- proof -
- from X_in Y_in tag_eq
- obtain x y where x_in: "x \<in> X" and y_in: "y \<in> Y" and eq_tg: "tag x = tag y"
- unfolding quotient_def Image_def str_eq_rel_def str_eq_def image_def
- apply simp by blast
- from same_tag_eqvt [OF eq_tg] have "x \<approx>Lang y" .
- with X_in Y_in x_in y_in
- show ?thesis by (auto simp:quotient_def str_eq_rel_def str_eq_def)
- qed
- } thus ?thesis unfolding inj_on_def by auto
- qed
- qed
-qed
-
-subsection {* The proof*}
-
-text {*
- Each case is given in a separate section, as well as the final main lemma. Detailed explainations accompanied by
- illustrations are given for non-trivial cases.
-
- For ever inductive case, there are two tasks, the easier one is to show the range finiteness of
- of the tagging function based on the finiteness of component partitions, the
- difficult one is to show that strings with the same tag are equivalent with respect to the
- composite language. Suppose the composite language be @{text "Lang"}, tagging function be
- @{text "tag"}, it amounts to show:
- \[
- @{text "tag(x) = tag(y) \<Longrightarrow> x \<approx>Lang y"}
- \]
- expanding the definition of @{text "\<approx>Lang"}, it amounts to show:
- \[
- @{text "tag(x) = tag(y) \<Longrightarrow> (\<forall> z. x@z \<in> Lang \<longleftrightarrow> y@z \<in> Lang)"}
- \]
- Because the assumed tag equlity @{text "tag(x) = tag(y)"} is symmetric,
- it is suffcient to show just one direction:
- \[
- @{text "\<And> x y z. \<lbrakk>tag(x) = tag(y); x@z \<in> Lang\<rbrakk> \<Longrightarrow> y@z \<in> Lang"}
- \]
- This is the pattern followed by every inductive case.
- *}
-
-subsubsection {* The base case for @{const "NULL"} *}
-
-lemma quot_null_eq:
- shows "(UNIV // \<approx>{}) = ({UNIV}::lang set)"
- unfolding quotient_def Image_def str_eq_rel_def by auto
-
-lemma quot_null_finiteI [intro]:
- shows "finite ((UNIV // \<approx>{})::lang set)"
-unfolding quot_null_eq by simp
-
-
-subsubsection {* The base case for @{const "EMPTY"} *}
-
-
-lemma quot_empty_subset:
- "UNIV // (\<approx>{[]}) \<subseteq> {{[]}, UNIV - {[]}}"
-proof
- fix x
- assume "x \<in> UNIV // \<approx>{[]}"
- then obtain y where h: "x = {z. (y, z) \<in> \<approx>{[]}}"
- unfolding quotient_def Image_def by blast
- show "x \<in> {{[]}, UNIV - {[]}}"
- proof (cases "y = []")
- case True with h
- have "x = {[]}" by (auto simp: str_eq_rel_def)
- thus ?thesis by simp
- next
- case False with h
- have "x = UNIV - {[]}" by (auto simp: str_eq_rel_def)
- thus ?thesis by simp
- qed
-qed
-
-lemma quot_empty_finiteI [intro]:
- shows "finite (UNIV // (\<approx>{[]}))"
-by (rule finite_subset[OF quot_empty_subset]) (simp)
-
-
-subsubsection {* The base case for @{const "CHAR"} *}
-
-lemma quot_char_subset:
- "UNIV // (\<approx>{[c]}) \<subseteq> {{[]},{[c]}, UNIV - {[], [c]}}"
-proof
- fix x
- assume "x \<in> UNIV // \<approx>{[c]}"
- then obtain y where h: "x = {z. (y, z) \<in> \<approx>{[c]}}"
- unfolding quotient_def Image_def by blast
- show "x \<in> {{[]},{[c]}, UNIV - {[], [c]}}"
- proof -
- { assume "y = []" hence "x = {[]}" using h
- by (auto simp:str_eq_rel_def)
- } moreover {
- assume "y = [c]" hence "x = {[c]}" using h
- by (auto dest!:spec[where x = "[]"] simp:str_eq_rel_def)
- } moreover {
- assume "y \<noteq> []" and "y \<noteq> [c]"
- hence "\<forall> z. (y @ z) \<noteq> [c]" by (case_tac y, auto)
- moreover have "\<And> p. (p \<noteq> [] \<and> p \<noteq> [c]) = (\<forall> q. p @ q \<noteq> [c])"
- by (case_tac p, auto)
- ultimately have "x = UNIV - {[],[c]}" using h
- by (auto simp add:str_eq_rel_def)
- } ultimately show ?thesis by blast
- qed
-qed
-
-lemma quot_char_finiteI [intro]:
- shows "finite (UNIV // (\<approx>{[c]}))"
-by (rule finite_subset[OF quot_char_subset]) (simp)
-
-
-subsubsection {* The inductive case for @{const ALT} *}
-
-definition
- tag_str_ALT :: "lang \<Rightarrow> lang \<Rightarrow> string \<Rightarrow> (lang \<times> lang)"
-where
- "tag_str_ALT L1 L2 = (\<lambda>x. (\<approx>L1 `` {x}, \<approx>L2 `` {x}))"
-
-lemma quot_union_finiteI [intro]:
- fixes L1 L2::"lang"
- assumes finite1: "finite (UNIV // \<approx>L1)"
- and finite2: "finite (UNIV // \<approx>L2)"
- shows "finite (UNIV // \<approx>(L1 \<union> L2))"
-proof (rule_tac tag = "tag_str_ALT L1 L2" in tag_finite_imageD)
- show "\<And>x y. tag_str_ALT L1 L2 x = tag_str_ALT L1 L2 y \<Longrightarrow> x \<approx>(L1 \<union> L2) y"
- unfolding tag_str_ALT_def
- unfolding str_eq_def
- unfolding Image_def
- unfolding str_eq_rel_def
- by auto
-next
- have *: "finite ((UNIV // \<approx>L1) \<times> (UNIV // \<approx>L2))"
- using finite1 finite2 by auto
- show "finite (range (tag_str_ALT L1 L2))"
- unfolding tag_str_ALT_def
- apply(rule finite_subset[OF _ *])
- unfolding quotient_def
- by auto
-qed
-
-subsubsection {* The inductive case for @{text "SEQ"}*}
-
-text {*
- For case @{const "SEQ"}, the language @{text "L"} is @{text "L\<^isub>1 ;; L\<^isub>2"}.
- Given @{text "x @ z \<in> L\<^isub>1 ;; L\<^isub>2"}, according to the defintion of @{text " L\<^isub>1 ;; L\<^isub>2"},
- string @{text "x @ z"} can be splitted with the prefix in @{text "L\<^isub>1"} and suffix in @{text "L\<^isub>2"}.
- The split point can either be in @{text "x"} (as shown in Fig. \ref{seq_first_split}),
- or in @{text "z"} (as shown in Fig. \ref{seq_snd_split}). Whichever way it goes, the structure
- on @{text "x @ z"} cn be transfered faithfully onto @{text "y @ z"}
- (as shown in Fig. \ref{seq_trans_first_split} and \ref{seq_trans_snd_split}) with the the help of the assumed
- tag equality. The following tag function @{text "tag_str_SEQ"} is such designed to facilitate
- such transfers and lemma @{text "tag_str_SEQ_injI"} formalizes the informal argument above. The details
- of structure transfer will be given their.
-\input{fig_seq}
-
+ It is now the time for use to discuss further about the way.
*}
-definition
- tag_str_SEQ :: "lang \<Rightarrow> lang \<Rightarrow> string \<Rightarrow> (lang \<times> lang set)"
-where
- "tag_str_SEQ L1 L2 =
- (\<lambda>x. (\<approx>L1 `` {x}, {(\<approx>L2 `` {x - xa}) | xa. xa \<le> x \<and> xa \<in> L1}))"
-
-text {* The following is a techical lemma which helps to split the @{text "x @ z \<in> L\<^isub>1 ;; L\<^isub>2"} mentioned above.*}
-
-lemma append_seq_elim:
- assumes "x @ y \<in> L\<^isub>1 ;; L\<^isub>2"
- shows "(\<exists> xa \<le> x. xa \<in> L\<^isub>1 \<and> (x - xa) @ y \<in> L\<^isub>2) \<or>
- (\<exists> ya \<le> y. (x @ ya) \<in> L\<^isub>1 \<and> (y - ya) \<in> L\<^isub>2)"
-proof-
- from assms obtain s\<^isub>1 s\<^isub>2
- where eq_xys: "x @ y = s\<^isub>1 @ s\<^isub>2"
- and in_seq: "s\<^isub>1 \<in> L\<^isub>1 \<and> s\<^isub>2 \<in> L\<^isub>2"
- by (auto simp:Seq_def)
- from app_eq_dest [OF eq_xys]
- have
- "(x \<le> s\<^isub>1 \<and> (s\<^isub>1 - x) @ s\<^isub>2 = y) \<or> (s\<^isub>1 \<le> x \<and> (x - s\<^isub>1) @ y = s\<^isub>2)"
- (is "?Split1 \<or> ?Split2") .
- moreover have "?Split1 \<Longrightarrow> \<exists> ya \<le> y. (x @ ya) \<in> L\<^isub>1 \<and> (y - ya) \<in> L\<^isub>2"
- using in_seq by (rule_tac x = "s\<^isub>1 - x" in exI, auto elim:prefixE)
- moreover have "?Split2 \<Longrightarrow> \<exists> xa \<le> x. xa \<in> L\<^isub>1 \<and> (x - xa) @ y \<in> L\<^isub>2"
- using in_seq by (rule_tac x = s\<^isub>1 in exI, auto)
- ultimately show ?thesis by blast
-qed
-
-
-lemma tag_str_SEQ_injI:
- fixes v w
- assumes eq_tag: "tag_str_SEQ L\<^isub>1 L\<^isub>2 v = tag_str_SEQ L\<^isub>1 L\<^isub>2 w"
- shows "v \<approx>(L\<^isub>1 ;; L\<^isub>2) w"
-proof-
- -- {* As explained before, a pattern for just one direction needs to be dealt with:*}
- { fix x y z
- assume xz_in_seq: "x @ z \<in> L\<^isub>1 ;; L\<^isub>2"
- and tag_xy: "tag_str_SEQ L\<^isub>1 L\<^isub>2 x = tag_str_SEQ L\<^isub>1 L\<^isub>2 y"
- have"y @ z \<in> L\<^isub>1 ;; L\<^isub>2"
- proof-
- -- {* There are two ways to split @{text "x@z"}: *}
- from append_seq_elim [OF xz_in_seq]
- have "(\<exists> xa \<le> x. xa \<in> L\<^isub>1 \<and> (x - xa) @ z \<in> L\<^isub>2) \<or>
- (\<exists> za \<le> z. (x @ za) \<in> L\<^isub>1 \<and> (z - za) \<in> L\<^isub>2)" .
- -- {* It can be shown that @{text "?thesis"} holds in either case: *}
- moreover {
- -- {* The case for the first split:*}
- fix xa
- assume h1: "xa \<le> x" and h2: "xa \<in> L\<^isub>1" and h3: "(x - xa) @ z \<in> L\<^isub>2"
- -- {* The following subgoal implements the structure transfer:*}
- obtain ya
- where "ya \<le> y"
- and "ya \<in> L\<^isub>1"
- and "(y - ya) @ z \<in> L\<^isub>2"
- proof -
- -- {*
- \begin{minipage}{0.8\textwidth}
- By expanding the definition of
- @{thm [display] "tag_xy"}
- and extracting the second compoent, we get:
- \end{minipage}
- *}
- have "{\<approx>L\<^isub>2 `` {x - xa} |xa. xa \<le> x \<and> xa \<in> L\<^isub>1} =
- {\<approx>L\<^isub>2 `` {y - ya} |ya. ya \<le> y \<and> ya \<in> L\<^isub>1}" (is "?Left = ?Right")
- using tag_xy unfolding tag_str_SEQ_def by simp
- -- {* Since @{thm "h1"} and @{thm "h2"} hold, it is not difficult to show: *}
- moreover have "\<approx>L\<^isub>2 `` {x - xa} \<in> ?Left" using h1 h2 by auto
- -- {*
- \begin{minipage}{0.7\textwidth}
- Through tag equality, equivalent class @{term "\<approx>L\<^isub>2 `` {x - xa}"} also
- belongs to the @{text "?Right"}:
- \end{minipage}
- *}
- ultimately have "\<approx>L\<^isub>2 `` {x - xa} \<in> ?Right" by simp
- -- {* From this, the counterpart of @{text "xa"} in @{text "y"} is obtained:*}
- then obtain ya
- where eq_xya: "\<approx>L\<^isub>2 `` {x - xa} = \<approx>L\<^isub>2 `` {y - ya}"
- and pref_ya: "ya \<le> y" and ya_in: "ya \<in> L\<^isub>1"
- by simp blast
- -- {* It can be proved that @{text "ya"} has the desired property:*}
- have "(y - ya)@z \<in> L\<^isub>2"
- proof -
- from eq_xya have "(x - xa) \<approx>L\<^isub>2 (y - ya)"
- unfolding Image_def str_eq_rel_def str_eq_def by auto
- with h3 show ?thesis unfolding str_eq_rel_def str_eq_def by simp
- qed
- -- {* Now, @{text "ya"} has all properties to be a qualified candidate:*}
- with pref_ya ya_in
- show ?thesis using that by blast
- qed
- -- {* From the properties of @{text "ya"}, @{text "y @ z \<in> L\<^isub>1 ;; L\<^isub>2"} is derived easily.*}
- hence "y @ z \<in> L\<^isub>1 ;; L\<^isub>2" by (erule_tac prefixE, auto simp:Seq_def)
- } moreover {
- -- {* The other case is even more simpler: *}
- fix za
- assume h1: "za \<le> z" and h2: "(x @ za) \<in> L\<^isub>1" and h3: "z - za \<in> L\<^isub>2"
- have "y @ za \<in> L\<^isub>1"
- proof-
- have "\<approx>L\<^isub>1 `` {x} = \<approx>L\<^isub>1 `` {y}"
- using tag_xy unfolding tag_str_SEQ_def by simp
- with h2 show ?thesis
- unfolding Image_def str_eq_rel_def str_eq_def by auto
- qed
- with h1 h3 have "y @ z \<in> L\<^isub>1 ;; L\<^isub>2"
- by (drule_tac A = L\<^isub>1 in seq_intro, auto elim:prefixE)
- }
- ultimately show ?thesis by blast
- qed
- }
- -- {*
- \begin{minipage}{0.8\textwidth}
- @{text "?thesis"} is proved by exploiting the symmetry of
- @{thm [source] "eq_tag"}:
- \end{minipage}
- *}
- from this [OF _ eq_tag] and this [OF _ eq_tag [THEN sym]]
- show ?thesis unfolding str_eq_def str_eq_rel_def by blast
-qed
-
-lemma quot_seq_finiteI [intro]:
- fixes L1 L2::"lang"
- assumes fin1: "finite (UNIV // \<approx>L1)"
- and fin2: "finite (UNIV // \<approx>L2)"
- shows "finite (UNIV // \<approx>(L1 ;; L2))"
-proof (rule_tac tag = "tag_str_SEQ L1 L2" in tag_finite_imageD)
- show "\<And>x y. tag_str_SEQ L1 L2 x = tag_str_SEQ L1 L2 y \<Longrightarrow> x \<approx>(L1 ;; L2) y"
- by (rule tag_str_SEQ_injI)
-next
- have *: "finite ((UNIV // \<approx>L1) \<times> (Pow (UNIV // \<approx>L2)))"
- using fin1 fin2 by auto
- show "finite (range (tag_str_SEQ L1 L2))"
- unfolding tag_str_SEQ_def
- apply(rule finite_subset[OF _ *])
- unfolding quotient_def
- by auto
-qed
-
-subsubsection {* The inductive case for @{const "STAR"} *}
-
-text {*
- This turned out to be the trickiest case. The essential goal is
- to proved @{text "y @ z \<in> L\<^isub>1*"} under the assumptions that @{text "x @ z \<in> L\<^isub>1*"}
- and that @{text "x"} and @{text "y"} have the same tag. The reasoning goes as the following:
- \begin{enumerate}
- \item Since @{text "x @ z \<in> L\<^isub>1*"} holds, a prefix @{text "xa"} of @{text "x"} can be found
- such that @{text "xa \<in> L\<^isub>1*"} and @{text "(x - xa)@z \<in> L\<^isub>1*"}, as shown in Fig. \ref{first_split}.
- Such a prefix always exists, @{text "xa = []"}, for example, is one.
- \item There could be many but fintie many of such @{text "xa"}, from which we can find the longest
- and name it @{text "xa_max"}, as shown in Fig. \ref{max_split}.
- \item The next step is to split @{text "z"} into @{text "za"} and @{text "zb"} such that
- @{text "(x - xa_max) @ za \<in> L\<^isub>1"} and @{text "zb \<in> L\<^isub>1*"} as shown in Fig. \ref{last_split}.
- Such a split always exists because:
- \begin{enumerate}
- \item Because @{text "(x - x_max) @ z \<in> L\<^isub>1*"}, it can always be splitted into prefix @{text "a"}
- and suffix @{text "b"}, such that @{text "a \<in> L\<^isub>1"} and @{text "b \<in> L\<^isub>1*"},
- as shown in Fig. \ref{ab_split}.
- \item But the prefix @{text "a"} CANNOT be shorter than @{text "x - xa_max"}
- (as shown in Fig. \ref{ab_split_wrong}), becasue otherwise,
- @{text "ma_max@a"} would be in the same kind as @{text "xa_max"} but with
- a larger size, conflicting with the fact that @{text "xa_max"} is the longest.
- \end{enumerate}
- \item \label{tansfer_step}
- By the assumption that @{text "x"} and @{text "y"} have the same tag, the structure on @{text "x @ z"}
- can be transferred to @{text "y @ z"} as shown in Fig. \ref{trans_split}. The detailed steps are:
- \begin{enumerate}
- \item A @{text "y"}-prefix @{text "ya"} corresponding to @{text "xa"} can be found,
- which satisfies conditions: @{text "ya \<in> L\<^isub>1*"} and @{text "(y - ya)@za \<in> L\<^isub>1"}.
- \item Since we already know @{text "zb \<in> L\<^isub>1*"}, we get @{text "(y - ya)@za@zb \<in> L\<^isub>1*"},
- and this is just @{text "(y - ya)@z \<in> L\<^isub>1*"}.
- \item With fact @{text "ya \<in> L\<^isub>1*"}, we finally get @{text "y@z \<in> L\<^isub>1*"}.
- \end{enumerate}
- \end{enumerate}
-
- The formal proof of lemma @{text "tag_str_STAR_injI"} faithfully follows this informal argument
- while the tagging function @{text "tag_str_STAR"} is defined to make the transfer in step
- \ref{ansfer_step} feasible.
-
- \input{fig_star}
-*}
-
-definition
- tag_str_STAR :: "lang \<Rightarrow> string \<Rightarrow> lang set"
-where
- "tag_str_STAR L1 = (\<lambda>x. {\<approx>L1 `` {x - xa} | xa. xa < x \<and> xa \<in> L1\<star>})"
-
-text {* A technical lemma. *}
-lemma finite_set_has_max: "\<lbrakk>finite A; A \<noteq> {}\<rbrakk> \<Longrightarrow>
- (\<exists> max \<in> A. \<forall> a \<in> A. f a <= (f max :: nat))"
-proof (induct rule:finite.induct)
- case emptyI thus ?case by simp
-next
- case (insertI A a)
- show ?case
- proof (cases "A = {}")
- case True thus ?thesis by (rule_tac x = a in bexI, auto)
- next
- case False
- with insertI.hyps and False
- obtain max
- where h1: "max \<in> A"
- and h2: "\<forall>a\<in>A. f a \<le> f max" by blast
- show ?thesis
- proof (cases "f a \<le> f max")
- assume "f a \<le> f max"
- with h1 h2 show ?thesis by (rule_tac x = max in bexI, auto)
- next
- assume "\<not> (f a \<le> f max)"
- thus ?thesis using h2 by (rule_tac x = a in bexI, auto)
- qed
- qed
-qed
-
-
-text {* The following is a technical lemma.which helps to show the range finiteness of tag function. *}
-lemma finite_strict_prefix_set: "finite {xa. xa < (x::string)}"
-apply (induct x rule:rev_induct, simp)
-apply (subgoal_tac "{xa. xa < xs @ [x]} = {xa. xa < xs} \<union> {xs}")
-by (auto simp:strict_prefix_def)
-
-
-lemma tag_str_STAR_injI:
- fixes v w
- assumes eq_tag: "tag_str_STAR L\<^isub>1 v = tag_str_STAR L\<^isub>1 w"
- shows "(v::string) \<approx>(L\<^isub>1\<star>) w"
-proof-
- -- {* As explained before, a pattern for just one direction needs to be dealt with:*}
- { fix x y z
- assume xz_in_star: "x @ z \<in> L\<^isub>1\<star>"
- and tag_xy: "tag_str_STAR L\<^isub>1 x = tag_str_STAR L\<^isub>1 y"
- have "y @ z \<in> L\<^isub>1\<star>"
- proof(cases "x = []")
- -- {*
- The degenerated case when @{text "x"} is a null string is easy to prove:
- *}
- case True
- with tag_xy have "y = []"
- by (auto simp add: tag_str_STAR_def strict_prefix_def)
- thus ?thesis using xz_in_star True by simp
- next
- -- {* The nontrival case:
- *}
- case False
- -- {*
- \begin{minipage}{0.8\textwidth}
- Since @{text "x @ z \<in> L\<^isub>1\<star>"}, @{text "x"} can always be splitted
- by a prefix @{text "xa"} together with its suffix @{text "x - xa"}, such
- that both @{text "xa"} and @{text "(x - xa) @ z"} are in @{text "L\<^isub>1\<star>"},
- and there could be many such splittings.Therefore, the following set @{text "?S"}
- is nonempty, and finite as well:
- \end{minipage}
- *}
- let ?S = "{xa. xa < x \<and> xa \<in> L\<^isub>1\<star> \<and> (x - xa) @ z \<in> L\<^isub>1\<star>}"
- have "finite ?S"
- by (rule_tac B = "{xa. xa < x}" in finite_subset,
- auto simp:finite_strict_prefix_set)
- moreover have "?S \<noteq> {}" using False xz_in_star
- by (simp, rule_tac x = "[]" in exI, auto simp:strict_prefix_def)
- -- {* \begin{minipage}{0.7\textwidth}
- Since @{text "?S"} is finite, we can always single out the longest and name it @{text "xa_max"}:
- \end{minipage}
- *}
- ultimately have "\<exists> xa_max \<in> ?S. \<forall> xa \<in> ?S. length xa \<le> length xa_max"
- using finite_set_has_max by blast
- then obtain xa_max
- where h1: "xa_max < x"
- and h2: "xa_max \<in> L\<^isub>1\<star>"
- and h3: "(x - xa_max) @ z \<in> L\<^isub>1\<star>"
- and h4:"\<forall> xa < x. xa \<in> L\<^isub>1\<star> \<and> (x - xa) @ z \<in> L\<^isub>1\<star>
- \<longrightarrow> length xa \<le> length xa_max"
- by blast
- -- {*
- \begin{minipage}{0.8\textwidth}
- By the equality of tags, the counterpart of @{text "xa_max"} among
- @{text "y"}-prefixes, named @{text "ya"}, can be found:
- \end{minipage}
- *}
- obtain ya
- where h5: "ya < y" and h6: "ya \<in> L\<^isub>1\<star>"
- and eq_xya: "(x - xa_max) \<approx>L\<^isub>1 (y - ya)"
- proof-
- from tag_xy have "{\<approx>L\<^isub>1 `` {x - xa} |xa. xa < x \<and> xa \<in> L\<^isub>1\<star>} =
- {\<approx>L\<^isub>1 `` {y - xa} |xa. xa < y \<and> xa \<in> L\<^isub>1\<star>}" (is "?left = ?right")
- by (auto simp:tag_str_STAR_def)
- moreover have "\<approx>L\<^isub>1 `` {x - xa_max} \<in> ?left" using h1 h2 by auto
- ultimately have "\<approx>L\<^isub>1 `` {x - xa_max} \<in> ?right" by simp
- thus ?thesis using that
- apply (simp add:Image_def str_eq_rel_def str_eq_def) by blast
- qed
- -- {*
- \begin{minipage}{0.8\textwidth}
- The @{text "?thesis"}, @{prop "y @ z \<in> L\<^isub>1\<star>"}, is a simple consequence
- of the following proposition:
- \end{minipage}
- *}
- have "(y - ya) @ z \<in> L\<^isub>1\<star>"
- proof-
- -- {* The idea is to split the suffix @{text "z"} into @{text "za"} and @{text "zb"},
- such that: *}
- obtain za zb where eq_zab: "z = za @ zb"
- and l_za: "(y - ya)@za \<in> L\<^isub>1" and ls_zb: "zb \<in> L\<^isub>1\<star>"
- proof -
- -- {*
- \begin{minipage}{0.8\textwidth}
- Since @{thm "h1"}, @{text "x"} can be splitted into
- @{text "a"} and @{text "b"} such that:
- \end{minipage}
- *}
- from h1 have "(x - xa_max) @ z \<noteq> []"
- by (auto simp:strict_prefix_def elim:prefixE)
- from star_decom [OF h3 this]
- obtain a b where a_in: "a \<in> L\<^isub>1"
- and a_neq: "a \<noteq> []" and b_in: "b \<in> L\<^isub>1\<star>"
- and ab_max: "(x - xa_max) @ z = a @ b" by blast
- -- {* Now the candiates for @{text "za"} and @{text "zb"} are found:*}
- let ?za = "a - (x - xa_max)" and ?zb = "b"
- have pfx: "(x - xa_max) \<le> a" (is "?P1")
- and eq_z: "z = ?za @ ?zb" (is "?P2")
- proof -
- -- {*
- \begin{minipage}{0.8\textwidth}
- Since @{text "(x - xa_max) @ z = a @ b"}, string @{text "(x - xa_max) @ z"}
- can be splitted in two ways:
- \end{minipage}
- *}
- have "((x - xa_max) \<le> a \<and> (a - (x - xa_max)) @ b = z) \<or>
- (a < (x - xa_max) \<and> ((x - xa_max) - a) @ z = b)"
- using app_eq_dest[OF ab_max] by (auto simp:strict_prefix_def)
- moreover {
- -- {* However, the undsired way can be refuted by absurdity: *}
- assume np: "a < (x - xa_max)"
- and b_eqs: "((x - xa_max) - a) @ z = b"
- have "False"
- proof -
- let ?xa_max' = "xa_max @ a"
- have "?xa_max' < x"
- using np h1 by (clarsimp simp:strict_prefix_def diff_prefix)
- moreover have "?xa_max' \<in> L\<^isub>1\<star>"
- using a_in h2 by (simp add:star_intro3)
- moreover have "(x - ?xa_max') @ z \<in> L\<^isub>1\<star>"
- using b_eqs b_in np h1 by (simp add:diff_diff_appd)
- moreover have "\<not> (length ?xa_max' \<le> length xa_max)"
- using a_neq by simp
- ultimately show ?thesis using h4 by blast
- qed }
- -- {* Now it can be shown that the splitting goes the way we desired. *}
- ultimately show ?P1 and ?P2 by auto
- qed
- hence "(x - xa_max)@?za \<in> L\<^isub>1" using a_in by (auto elim:prefixE)
- -- {* Now candidates @{text "?za"} and @{text "?zb"} have all the requred properteis. *}
- with eq_xya have "(y - ya) @ ?za \<in> L\<^isub>1"
- by (auto simp:str_eq_def str_eq_rel_def)
- with eq_z and b_in
- show ?thesis using that by blast
- qed
- -- {*
- @{text "?thesis"} can easily be shown using properties of @{text "za"} and @{text "zb"}:
- *}
- have "((y - ya) @ za) @ zb \<in> L\<^isub>1\<star>" using l_za ls_zb by blast
- with eq_zab show ?thesis by simp
- qed
- with h5 h6 show ?thesis
- by (drule_tac star_intro1, auto simp:strict_prefix_def elim:prefixE)
- qed
- }
- -- {* By instantiating the reasoning pattern just derived for both directions:*}
- from this [OF _ eq_tag] and this [OF _ eq_tag [THEN sym]]
- -- {* The thesis is proved as a trival consequence: *}
- show ?thesis unfolding str_eq_def str_eq_rel_def by blast
-qed
-
-lemma -- {* The oringal version with less explicit details. *}
- fixes v w
- assumes eq_tag: "tag_str_STAR L\<^isub>1 v = tag_str_STAR L\<^isub>1 w"
- shows "(v::string) \<approx>(L\<^isub>1\<star>) w"
-proof-
- -- {*
- \begin{minipage}{0.8\textwidth}
- According to the definition of @{text "\<approx>Lang"},
- proving @{text "v \<approx>(L\<^isub>1\<star>) w"} amounts to
- showing: for any string @{text "u"},
- if @{text "v @ u \<in> (L\<^isub>1\<star>)"} then @{text "w @ u \<in> (L\<^isub>1\<star>)"} and vice versa.
- The reasoning pattern for both directions are the same, as derived
- in the following:
- \end{minipage}
- *}
- { fix x y z
- assume xz_in_star: "x @ z \<in> L\<^isub>1\<star>"
- and tag_xy: "tag_str_STAR L\<^isub>1 x = tag_str_STAR L\<^isub>1 y"
- have "y @ z \<in> L\<^isub>1\<star>"
- proof(cases "x = []")
- -- {*
- The degenerated case when @{text "x"} is a null string is easy to prove:
- *}
- case True
- with tag_xy have "y = []"
- by (auto simp:tag_str_STAR_def strict_prefix_def)
- thus ?thesis using xz_in_star True by simp
- next
- -- {*
- \begin{minipage}{0.8\textwidth}
- The case when @{text "x"} is not null, and
- @{text "x @ z"} is in @{text "L\<^isub>1\<star>"},
- \end{minipage}
- *}
- case False
- obtain x_max
- where h1: "x_max < x"
- and h2: "x_max \<in> L\<^isub>1\<star>"
- and h3: "(x - x_max) @ z \<in> L\<^isub>1\<star>"
- and h4:"\<forall> xa < x. xa \<in> L\<^isub>1\<star> \<and> (x - xa) @ z \<in> L\<^isub>1\<star>
- \<longrightarrow> length xa \<le> length x_max"
- proof-
- let ?S = "{xa. xa < x \<and> xa \<in> L\<^isub>1\<star> \<and> (x - xa) @ z \<in> L\<^isub>1\<star>}"
- have "finite ?S"
- by (rule_tac B = "{xa. xa < x}" in finite_subset,
- auto simp:finite_strict_prefix_set)
- moreover have "?S \<noteq> {}" using False xz_in_star
- by (simp, rule_tac x = "[]" in exI, auto simp:strict_prefix_def)
- ultimately have "\<exists> max \<in> ?S. \<forall> a \<in> ?S. length a \<le> length max"
- using finite_set_has_max by blast
- thus ?thesis using that by blast
- qed
- obtain ya
- where h5: "ya < y" and h6: "ya \<in> L\<^isub>1\<star>" and h7: "(x - x_max) \<approx>L\<^isub>1 (y - ya)"
- proof-
- from tag_xy have "{\<approx>L\<^isub>1 `` {x - xa} |xa. xa < x \<and> xa \<in> L\<^isub>1\<star>} =
- {\<approx>L\<^isub>1 `` {y - xa} |xa. xa < y \<and> xa \<in> L\<^isub>1\<star>}" (is "?left = ?right")
- by (auto simp:tag_str_STAR_def)
- moreover have "\<approx>L\<^isub>1 `` {x - x_max} \<in> ?left" using h1 h2 by auto
- ultimately have "\<approx>L\<^isub>1 `` {x - x_max} \<in> ?right" by simp
- with that show ?thesis apply
- (simp add:Image_def str_eq_rel_def str_eq_def) by blast
- qed
- have "(y - ya) @ z \<in> L\<^isub>1\<star>"
- proof-
- from h3 h1 obtain a b where a_in: "a \<in> L\<^isub>1"
- and a_neq: "a \<noteq> []" and b_in: "b \<in> L\<^isub>1\<star>"
- and ab_max: "(x - x_max) @ z = a @ b"
- by (drule_tac star_decom, auto simp:strict_prefix_def elim:prefixE)
- have "(x - x_max) \<le> a \<and> (a - (x - x_max)) @ b = z"
- proof -
- have "((x - x_max) \<le> a \<and> (a - (x - x_max)) @ b = z) \<or>
- (a < (x - x_max) \<and> ((x - x_max) - a) @ z = b)"
- using app_eq_dest[OF ab_max] by (auto simp:strict_prefix_def)
- moreover {
- assume np: "a < (x - x_max)" and b_eqs: " ((x - x_max) - a) @ z = b"
- have "False"
- proof -
- let ?x_max' = "x_max @ a"
- have "?x_max' < x"
- using np h1 by (clarsimp simp:strict_prefix_def diff_prefix)
- moreover have "?x_max' \<in> L\<^isub>1\<star>"
- using a_in h2 by (simp add:star_intro3)
- moreover have "(x - ?x_max') @ z \<in> L\<^isub>1\<star>"
- using b_eqs b_in np h1 by (simp add:diff_diff_appd)
- moreover have "\<not> (length ?x_max' \<le> length x_max)"
- using a_neq by simp
- ultimately show ?thesis using h4 by blast
- qed
- } ultimately show ?thesis by blast
- qed
- then obtain za where z_decom: "z = za @ b"
- and x_za: "(x - x_max) @ za \<in> L\<^isub>1"
- using a_in by (auto elim:prefixE)
- from x_za h7 have "(y - ya) @ za \<in> L\<^isub>1"
- by (auto simp:str_eq_def str_eq_rel_def)
- with b_in have "((y - ya) @ za) @ b \<in> L\<^isub>1\<star>" by blast
- with z_decom show ?thesis by auto
- qed
- with h5 h6 show ?thesis
- by (drule_tac star_intro1, auto simp:strict_prefix_def elim:prefixE)
- qed
- }
- -- {* By instantiating the reasoning pattern just derived for both directions:*}
- from this [OF _ eq_tag] and this [OF _ eq_tag [THEN sym]]
- -- {* The thesis is proved as a trival consequence: *}
- show ?thesis unfolding str_eq_def str_eq_rel_def by blast
-qed
-
-lemma quot_star_finiteI [intro]:
- fixes L1::"lang"
- assumes finite1: "finite (UNIV // \<approx>L1)"
- shows "finite (UNIV // \<approx>(L1\<star>))"
-proof (rule_tac tag = "tag_str_STAR L1" in tag_finite_imageD)
- show "\<And>x y. tag_str_STAR L1 x = tag_str_STAR L1 y \<Longrightarrow> x \<approx>(L1\<star>) y"
- by (rule tag_str_STAR_injI)
-next
- have *: "finite (Pow (UNIV // \<approx>L1))"
- using finite1 by auto
- show "finite (range (tag_str_STAR L1))"
- unfolding tag_str_STAR_def
- apply(rule finite_subset[OF _ *])
- unfolding quotient_def
- by auto
-qed
-
-subsubsection{* The conclusion *}
-
-lemma rexp_imp_finite:
- fixes r::"rexp"
- shows "finite (UNIV // \<approx>(L r))"
-by (induct r) (auto)
-
end