section ‹Lexicographic order on lists›
theory List_lexord
imports Main
begin
instantiation list :: (ord) ord
begin
definition
list_less_def: "xs < ys ⟷ (xs, ys) ∈ lexord {(u, v). u < v}"
definition
list_le_def: "(xs :: _ list) ≤ ys ⟷ xs < ys ∨ xs = ys"
instance ..
end
instance list :: (order) order
proof
fix xs :: "'a list"
show "xs ≤ xs" by (simp add: list_le_def)
next
fix xs ys zs :: "'a list"
assume "xs ≤ ys" and "ys ≤ zs"
then show "xs ≤ zs"
apply (auto simp add: list_le_def list_less_def)
apply (rule lexord_trans)
apply (auto intro: transI)
done
next
fix xs ys :: "'a list"
assume "xs ≤ ys" and "ys ≤ xs"
then show "xs = ys"
apply (auto simp add: list_le_def list_less_def)
apply (rule lexord_irreflexive [THEN notE])
defer
apply (rule lexord_trans)
apply (auto intro: transI)
done
next
fix xs ys :: "'a list"
show "xs < ys ⟷ xs ≤ ys ∧ ¬ ys ≤ xs"
apply (auto simp add: list_less_def list_le_def)
defer
apply (rule lexord_irreflexive [THEN notE])
apply auto
apply (rule lexord_irreflexive [THEN notE])
defer
apply (rule lexord_trans)
apply (auto intro: transI)
done
qed
instance list :: (linorder) linorder
proof
fix xs ys :: "'a list"
have "(xs, ys) ∈ lexord {(u, v). u < v} ∨ xs = ys ∨ (ys, xs) ∈ lexord {(u, v). u < v}"
by (rule lexord_linear) auto
then show "xs ≤ ys ∨ ys ≤ xs"
by (auto simp add: list_le_def list_less_def)
qed
instantiation list :: (linorder) distrib_lattice
begin
definition "(inf :: 'a list ⇒ _) = min"
definition "(sup :: 'a list ⇒ _) = max"
instance
by standard (auto simp add: inf_list_def sup_list_def max_min_distrib2)
end
lemma not_less_Nil [simp]: "¬ 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 ⟷ a < b ∨ a = b ∧ x < y"
by (simp add: list_less_def)
lemma le_Nil [simp]: "x ≤ [] ⟷ x = []"
unfolding list_le_def by (cases x) auto
lemma Nil_le_Cons [simp]: "[] ≤ x"
unfolding list_le_def by (cases x) auto
lemma Cons_le_Cons [simp]: "a # x ≤ b # y ⟷ a < b ∨ a = b ∧ x ≤ 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) ⟷ False"
"[] < (x::'a::{equal, order}) # xs ⟷ True"
"(x::'a::{equal, order}) # xs < y # ys ⟷ x < y ∨ x = y ∧ xs < ys"
by simp_all
lemma less_eq_list_code [code]:
"x # xs ≤ ([]::'a::{equal, order} list) ⟷ False"
"[] ≤ (xs::'a::{equal, order} list) ⟷ True"
"(x::'a::{equal, order}) # xs ≤ y # ys ⟷ x < y ∨ x = y ∧ xs ≤ ys"
by simp_all
end