Theory Sublist_Order

theory Sublist_Order
imports Sublist
(*  Title:      HOL/Library/Sublist_Order.thy
Authors: Peter Lammich, Uni Muenster <peter.lammich@uni-muenster.de>
Florian Haftmann, Tobias Nipkow, TU Muenchen
*)


header {* Sublist Ordering *}

theory Sublist_Order
imports Sublist
begin

text {*
This theory defines sublist ordering on lists.
A list @{text ys} is a sublist of a list @{text xs},
iff one obtains @{text ys} by erasing some elements from @{text xs}.
*}


subsection {* Definitions and basic lemmas *}

instantiation list :: (type) ord
begin

definition
"(xs :: 'a list) ≤ ys <-> sublisteq xs ys"

definition
"(xs :: 'a list) < ys <-> xs ≤ ys ∧ ¬ ys ≤ xs"

instance ..

end

instance list :: (type) order
proof
fix xs ys :: "'a list"
show "xs < ys <-> xs ≤ ys ∧ ¬ ys ≤ xs" unfolding less_list_def ..
next
fix xs :: "'a list"
show "xs ≤ xs" by (simp add: less_eq_list_def)
next
fix xs ys :: "'a list"
assume "xs <= ys" and "ys <= xs"
thus "xs = ys" by (unfold less_eq_list_def) (rule sublisteq_antisym)
next
fix xs ys zs :: "'a list"
assume "xs <= ys" and "ys <= zs"
thus "xs <= zs" by (unfold less_eq_list_def) (rule sublisteq_trans)
qed

lemmas less_eq_list_induct [consumes 1, case_names empty drop take] =
list_hembeq.induct [of "op =", folded less_eq_list_def]
lemmas less_eq_list_drop = list_hembeq.list_hembeq_Cons [of "op =", folded less_eq_list_def]
lemmas le_list_Cons2_iff [simp, code] = sublisteq_Cons2_iff [folded less_eq_list_def]
lemmas le_list_map = sublisteq_map [folded less_eq_list_def]
lemmas le_list_filter = sublisteq_filter [folded less_eq_list_def]
lemmas le_list_length = list_hembeq_length [of "op =", folded less_eq_list_def]

lemma less_list_length: "xs < ys ==> length xs < length ys"
by (metis list_hembeq_length sublisteq_same_length le_neq_implies_less less_list_def less_eq_list_def)

lemma less_list_empty [simp]: "[] < xs <-> xs ≠ []"
by (metis less_eq_list_def list_hembeq_Nil order_less_le)

lemma less_list_below_empty [simp]: "xs < [] <-> False"
by (metis list_hembeq_Nil less_eq_list_def less_list_def)

lemma less_list_drop: "xs < ys ==> xs < x # ys"
by (unfold less_le less_eq_list_def) (auto)

lemma less_list_take_iff: "x # xs < x # ys <-> xs < ys"
by (metis sublisteq_Cons2_iff less_list_def less_eq_list_def)

lemma less_list_drop_many: "xs < ys ==> xs < zs @ ys"
by (metis sublisteq_append_le_same_iff sublisteq_drop_many order_less_le self_append_conv2 less_eq_list_def)

lemma less_list_take_many_iff: "zs @ xs < zs @ ys <-> xs < ys"
by (metis less_list_def less_eq_list_def sublisteq_append')

lemma less_list_rev_take: "xs @ zs < ys @ zs <-> xs < ys"
by (unfold less_le less_eq_list_def) auto

end