New theory Library/List_Lenlexorder.thy, a type class instantiation for well-ordering lists
(* Title: HOL/Library/List_Lexorder.thy
Author: Norbert Voelker
*)
section \<open>Lexicographic order on lists\<close>
theory List_Lexorder
imports Main
begin
instantiation list :: (ord) ord
begin
definition
list_less_def: "xs < ys \<longleftrightarrow> (xs, ys) \<in> lexord {(u, v). u < v}"
definition
list_le_def: "(xs :: _ list) \<le> ys \<longleftrightarrow> xs < ys \<or> xs = ys"
instance ..
end
instance list :: (order) order
proof
let ?r = "{(u, v::'a). u < v}"
have tr: "trans ?r"
using trans_def by fastforce
have \<section>: False
if "(xs,ys) \<in> lexord ?r" "(ys,xs) \<in> lexord ?r" for xs ys :: "'a list"
proof -
have "(xs,xs) \<in> lexord ?r"
using that transD [OF lexord_transI [OF tr]] by blast
then show False
by (meson case_prodD lexord_irreflexive less_irrefl mem_Collect_eq)
qed
show "xs \<le> xs" for xs :: "'a list" by (simp add: list_le_def)
show "xs \<le> zs" if "xs \<le> ys" and "ys \<le> zs" for xs ys zs :: "'a list"
using that transD [OF lexord_transI [OF tr]] by (auto simp add: list_le_def list_less_def)
show "xs = ys" if "xs \<le> ys" "ys \<le> xs" for xs ys :: "'a list"
using \<section> that list_le_def list_less_def by blast
show "xs < ys \<longleftrightarrow> xs \<le> ys \<and> \<not> ys \<le> xs" for xs ys :: "'a list"
by (auto simp add: list_less_def list_le_def dest: \<section>)
qed
instance list :: (linorder) linorder
proof
fix xs ys :: "'a list"
have "total (lexord {(u, v::'a). u < v})"
by (rule total_lexord) (auto simp: total_on_def)
then show "xs \<le> ys \<or> ys \<le> xs"
by (auto simp add: total_on_def list_le_def list_less_def)
qed
instantiation list :: (linorder) distrib_lattice
begin
definition "(inf :: 'a list \<Rightarrow> _) = min"
definition "(sup :: 'a list \<Rightarrow> _) = max"
instance
by standard (auto simp add: inf_list_def sup_list_def max_min_distrib2)
end
lemma not_less_Nil [simp]: "\<not> x < []"
by (simp add: list_less_def)
lemma Nil_less_Cons [simp]: "[] < a # x"
by (simp add: list_less_def)
lemma Cons_less_Cons [simp]: "a # x < b # y \<longleftrightarrow> a < b \<or> a = b \<and> x < y"
by (simp add: list_less_def)
lemma le_Nil [simp]: "x \<le> [] \<longleftrightarrow> x = []"
unfolding list_le_def by (cases x) auto
lemma Nil_le_Cons [simp]: "[] \<le> x"
unfolding list_le_def by (cases x) auto
lemma Cons_le_Cons [simp]: "a # x \<le> b # y \<longleftrightarrow> a < b \<or> a = b \<and> x \<le> y"
unfolding list_le_def by auto
instantiation list :: (order) order_bot
begin
definition "bot = []"
instance
by standard (simp add: bot_list_def)
end
lemma less_list_code [code]:
"xs < ([]::'a::{equal, order} list) \<longleftrightarrow> False"
"[] < (x::'a::{equal, order}) # xs \<longleftrightarrow> True"
"(x::'a::{equal, order}) # xs < y # ys \<longleftrightarrow> x < y \<or> x = y \<and> xs < ys"
by simp_all
lemma less_eq_list_code [code]:
"x # xs \<le> ([]::'a::{equal, order} list) \<longleftrightarrow> False"
"[] \<le> (xs::'a::{equal, order} list) \<longleftrightarrow> True"
"(x::'a::{equal, order}) # xs \<le> y # ys \<longleftrightarrow> x < y \<or> x = y \<and> xs \<le> ys"
by simp_all
end