(*  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) \<le> ys \<longleftrightarrow> sublisteq xs ys"

definition

  "(xs :: 'a list) < ys \<longleftrightarrow> xs \<le> ys \<and> \<not> ys \<le> xs"

instance ..

end

instance list :: (type) order

proof

  fix xs ys :: "'a list"

  show "xs < ys \<longleftrightarrow> xs \<le> ys \<and> \<not> ys \<le> xs" unfolding less_list_def .. 

next

  fix xs :: "'a list"

  show "xs \<le> 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 \<Longrightarrow> 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 \<longleftrightarrow> xs \<noteq> []"

  by (metis less_eq_list_def list_hembeq_Nil order_less_le)

lemma less_list_below_empty [simp]: "xs < [] \<longleftrightarrow> False"

  by (metis list_hembeq_Nil less_eq_list_def less_list_def)

lemma less_list_drop: "xs < ys \<Longrightarrow> xs < x # ys"

  by (unfold less_le less_eq_list_def) (auto)

lemma less_list_take_iff: "x # xs < x # ys \<longleftrightarrow> xs < ys"

  by (metis sublisteq_Cons2_iff less_list_def less_eq_list_def)

lemma less_list_drop_many: "xs < ys \<Longrightarrow> 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 \<longleftrightarrow> xs < ys"

  by (metis less_list_def less_eq_list_def sublisteq_append')

lemma less_list_rev_take: "xs @ zs < ys @ zs \<longleftrightarrow> xs < ys"

  by (unfold less_le less_eq_list_def) auto

end