# Theory Order

```(*  Title:      ZF/Order.thy
Author:     Lawrence C Paulson, Cambridge University Computer Laboratory

Results from the book "Set Theory: an Introduction to Independence Proofs"
by Kenneth Kunen.  Chapter 1, section 6.
Additional definitions and lemmas for reflexive orders.
*)

section‹Partial and Total Orderings: Basic Definitions and Properties›

theory Order imports WF Perm begin

text ‹We adopt the following convention: ‹ord› is used for
strict orders and ‹order› is used for their reflexive
counterparts.›

definition
part_ord :: "[i,i]⇒o"                (*Strict partial ordering*)  where
"part_ord(A,r) ≡ irrefl(A,r) ∧ trans[A](r)"

definition
linear   :: "[i,i]⇒o"                (*Strict total ordering*)  where
"linear(A,r) ≡ (∀x∈A. ∀y∈A. ⟨x,y⟩:r | x=y | ⟨y,x⟩:r)"

definition
tot_ord  :: "[i,i]⇒o"                (*Strict total ordering*)  where
"tot_ord(A,r) ≡ part_ord(A,r) ∧ linear(A,r)"

definition
"preorder_on(A, r) ≡ refl(A, r) ∧ trans[A](r)"

definition                              (*Partial ordering*)
"partial_order_on(A, r) ≡ preorder_on(A, r) ∧ antisym(r)"

abbreviation
"Preorder(r) ≡ preorder_on(field(r), r)"

abbreviation
"Partial_order(r) ≡ partial_order_on(field(r), r)"

definition
well_ord :: "[i,i]⇒o"                (*Well-ordering*)  where
"well_ord(A,r) ≡ tot_ord(A,r) ∧ wf[A](r)"

definition
mono_map :: "[i,i,i,i]⇒i"            (*Order-preserving maps*)  where
"mono_map(A,r,B,s) ≡
{f ∈ A->B. ∀x∈A. ∀y∈A. ⟨x,y⟩:r ⟶ <f`x,f`y>:s}"

definition
ord_iso  :: "[i,i,i,i]⇒i"  (‹(⟨_, _⟩ ≅/ ⟨_, _⟩)› 51)  (*Order isomorphisms*)  where
"⟨A,r⟩ ≅ ⟨B,s⟩ ≡
{f ∈ bij(A,B). ∀x∈A. ∀y∈A. ⟨x,y⟩:r ⟷ <f`x,f`y>:s}"

definition
pred     :: "[i,i,i]⇒i"              (*Set of predecessors*)  where
"pred(A,x,r) ≡ {y ∈ A. ⟨y,x⟩:r}"

definition
ord_iso_map :: "[i,i,i,i]⇒i"         (*Construction for linearity theorem*)  where
"ord_iso_map(A,r,B,s) ≡
⋃x∈A. ⋃y∈B. ⋃f ∈ ord_iso(pred(A,x,r), r, pred(B,y,s), s). {⟨x,y⟩}"

definition
first :: "[i, i, i] ⇒ o"  where
"first(u, X, R) ≡ u ∈ X ∧ (∀v∈X. v≠u ⟶ ⟨u,v⟩ ∈ R)"

subsection‹Immediate Consequences of the Definitions›

lemma part_ord_Imp_asym:
"part_ord(A,r) ⟹ asym(r ∩ A*A)"
by (unfold part_ord_def irrefl_def trans_on_def asym_def, blast)

lemma linearE:
"⟦linear(A,r);  x ∈ A;  y ∈ A;
⟨x,y⟩:r ⟹ P;  x=y ⟹ P;  ⟨y,x⟩:r ⟹ P⟧
⟹ P"

(** General properties of well_ord **)

lemma well_ordI:
"⟦wf[A](r); linear(A,r)⟧ ⟹ well_ord(A,r)"
apply (simp add: irrefl_def part_ord_def tot_ord_def
trans_on_def well_ord_def wf_on_not_refl)
apply (fast elim: linearE wf_on_asym wf_on_chain3)
done

lemma well_ord_is_wf:
"well_ord(A,r) ⟹ wf[A](r)"
by (unfold well_ord_def, safe)

lemma well_ord_is_trans_on:
"well_ord(A,r) ⟹ trans[A](r)"
by (unfold well_ord_def tot_ord_def part_ord_def, safe)

lemma well_ord_is_linear: "well_ord(A,r) ⟹ linear(A,r)"
by (unfold well_ord_def tot_ord_def, blast)

(** Derived rules for pred(A,x,r) **)

lemma pred_iff: "y ∈ pred(A,x,r) ⟷ ⟨y,x⟩:r ∧ y ∈ A"
by (unfold pred_def, blast)

lemmas predI = conjI [THEN pred_iff [THEN iffD2]]

lemma predE: "⟦y ∈ pred(A,x,r);  ⟦y ∈ A; ⟨y,x⟩:r⟧ ⟹ P⟧ ⟹ P"

lemma pred_subset_under: "pred(A,x,r) ⊆ r -`` {x}"

lemma pred_subset: "pred(A,x,r) ⊆ A"

lemma pred_pred_eq:
"pred(pred(A,x,r), y, r) = pred(A,x,r) ∩ pred(A,y,r)"

lemma trans_pred_pred_eq:
"⟦trans[A](r);  ⟨y,x⟩:r;  x ∈ A;  y ∈ A⟧
⟹ pred(pred(A,x,r), y, r) = pred(A,y,r)"
by (unfold trans_on_def pred_def, blast)

subsection‹Restricting an Ordering's Domain›

(** The ordering's properties hold over all subsets of its domain
[including initial segments of the form pred(A,x,r) **)

(*Note: a relation s such that s<=r need not be a partial ordering*)
lemma part_ord_subset:
"⟦part_ord(A,r);  B<=A⟧ ⟹ part_ord(B,r)"
by (unfold part_ord_def irrefl_def trans_on_def, blast)

lemma linear_subset:
"⟦linear(A,r);  B<=A⟧ ⟹ linear(B,r)"
by (unfold linear_def, blast)

lemma tot_ord_subset:
"⟦tot_ord(A,r);  B<=A⟧ ⟹ tot_ord(B,r)"
unfolding tot_ord_def
apply (fast elim!: part_ord_subset linear_subset)
done

lemma well_ord_subset:
"⟦well_ord(A,r);  B<=A⟧ ⟹ well_ord(B,r)"
unfolding well_ord_def
apply (fast elim!: tot_ord_subset wf_on_subset_A)
done

(** Relations restricted to a smaller domain, by Krzysztof Grabczewski **)

lemma irrefl_Int_iff: "irrefl(A,r ∩ A*A) ⟷ irrefl(A,r)"
by (unfold irrefl_def, blast)

lemma trans_on_Int_iff: "trans[A](r ∩ A*A) ⟷ trans[A](r)"
by (unfold trans_on_def, blast)

lemma part_ord_Int_iff: "part_ord(A,r ∩ A*A) ⟷ part_ord(A,r)"
unfolding part_ord_def
done

lemma linear_Int_iff: "linear(A,r ∩ A*A) ⟷ linear(A,r)"
by (unfold linear_def, blast)

lemma tot_ord_Int_iff: "tot_ord(A,r ∩ A*A) ⟷ tot_ord(A,r)"
unfolding tot_ord_def
done

lemma wf_on_Int_iff: "wf[A](r ∩ A*A) ⟷ wf[A](r)"
apply (unfold wf_on_def wf_def, fast) (*10 times faster than blast!*)
done

lemma well_ord_Int_iff: "well_ord(A,r ∩ A*A) ⟷ well_ord(A,r)"
unfolding well_ord_def
done

subsection‹Empty and Unit Domains›

(*The empty relation is well-founded*)
lemma wf_on_any_0: "wf[A](0)"
by (simp add: wf_on_def wf_def, fast)

subsubsection‹Relations over the Empty Set›

lemma irrefl_0: "irrefl(0,r)"
by (unfold irrefl_def, blast)

lemma trans_on_0: "trans[0](r)"
by (unfold trans_on_def, blast)

lemma part_ord_0: "part_ord(0,r)"
unfolding part_ord_def
done

lemma linear_0: "linear(0,r)"
by (unfold linear_def, blast)

lemma tot_ord_0: "tot_ord(0,r)"
unfolding tot_ord_def
done

lemma wf_on_0: "wf[0](r)"
by (unfold wf_on_def wf_def, blast)

lemma well_ord_0: "well_ord(0,r)"
unfolding well_ord_def
done

subsubsection‹The Empty Relation Well-Orders the Unit Set›

text‹by Grabczewski›

lemma tot_ord_unit: "tot_ord({a},0)"
by (simp add: irrefl_def trans_on_def part_ord_def linear_def tot_ord_def)

lemma well_ord_unit: "well_ord({a},0)"
unfolding well_ord_def
done

subsection‹Order-Isomorphisms›

text‹Suppes calls them "similarities"›

(** Order-preserving (monotone) maps **)

lemma mono_map_is_fun: "f ∈ mono_map(A,r,B,s) ⟹ f ∈ A->B"

lemma mono_map_is_inj:
"⟦linear(A,r);  wf[B](s);  f ∈ mono_map(A,r,B,s)⟧ ⟹ f ∈ inj(A,B)"
apply (unfold mono_map_def inj_def, clarify)
apply (erule_tac x=w and y=x in linearE, assumption+)
apply (force intro: apply_type dest: wf_on_not_refl)+
done

lemma ord_isoI:
"⟦f ∈ bij(A, B);
⋀x y. ⟦x ∈ A; y ∈ A⟧ ⟹ ⟨x, y⟩ ∈ r ⟷ <f`x, f`y> ∈ s⟧
⟹ f ∈ ord_iso(A,r,B,s)"

lemma ord_iso_is_mono_map:
"f ∈ ord_iso(A,r,B,s) ⟹ f ∈ mono_map(A,r,B,s)"
apply (blast dest!: bij_is_fun)
done

lemma ord_iso_is_bij:
"f ∈ ord_iso(A,r,B,s) ⟹ f ∈ bij(A,B)"

(*Needed?  But ord_iso_converse is!*)
lemma ord_iso_apply:
"⟦f ∈ ord_iso(A,r,B,s);  ⟨x,y⟩: r;  x ∈ A;  y ∈ A⟧ ⟹ <f`x, f`y> ∈ s"

lemma ord_iso_converse:
"⟦f ∈ ord_iso(A,r,B,s);  ⟨x,y⟩: s;  x ∈ B;  y ∈ B⟧
⟹ <converse(f) ` x, converse(f) ` y> ∈ r"
apply (erule bspec [THEN bspec, THEN iffD2])
apply (erule asm_rl bij_converse_bij [THEN bij_is_fun, THEN apply_type])+
done

(** Symmetry and Transitivity Rules **)

(*Reflexivity of similarity*)
lemma ord_iso_refl: "id(A): ord_iso(A,r,A,r)"
by (rule id_bij [THEN ord_isoI], simp)

(*Symmetry of similarity*)
lemma ord_iso_sym: "f ∈ ord_iso(A,r,B,s) ⟹ converse(f): ord_iso(B,s,A,r)"
apply (auto simp add: right_inverse_bij bij_converse_bij
bij_is_fun [THEN apply_funtype])
done

(*Transitivity of similarity*)
lemma mono_map_trans:
"⟦g ∈ mono_map(A,r,B,s);  f ∈ mono_map(B,s,C,t)⟧
⟹ (f O g): mono_map(A,r,C,t)"
unfolding mono_map_def
done

(*Transitivity of similarity: the order-isomorphism relation*)
lemma ord_iso_trans:
"⟦g ∈ ord_iso(A,r,B,s);  f ∈ ord_iso(B,s,C,t)⟧
⟹ (f O g): ord_iso(A,r,C,t)"
apply (unfold ord_iso_def, clarify)
apply (frule bij_is_fun [of f])
apply (frule bij_is_fun [of g])
done

(** Two monotone maps can make an order-isomorphism **)

lemma mono_ord_isoI:
"⟦f ∈ mono_map(A,r,B,s);  g ∈ mono_map(B,s,A,r);
f O g = id(B);  g O f = id(A)⟧ ⟹ f ∈ ord_iso(A,r,B,s)"
apply (simp add: ord_iso_def mono_map_def, safe)
apply (intro fg_imp_bijective, auto)
apply (subgoal_tac "<g` (f`x), g` (f`y) > ∈ r")
apply (simp add: comp_eq_id_iff [THEN iffD1])
apply (blast intro: apply_funtype)
done

lemma well_ord_mono_ord_isoI:
"⟦well_ord(A,r);  well_ord(B,s);
f ∈ mono_map(A,r,B,s);  converse(f): mono_map(B,s,A,r)⟧
⟹ f ∈ ord_iso(A,r,B,s)"
apply (intro mono_ord_isoI, auto)
apply (frule mono_map_is_fun [THEN fun_is_rel])
apply (erule converse_converse [THEN subst], rule left_comp_inverse)
apply (blast intro: left_comp_inverse mono_map_is_inj well_ord_is_linear
well_ord_is_wf)+
done

(** Order-isomorphisms preserve the ordering's properties **)

lemma part_ord_ord_iso:
"⟦part_ord(B,s);  f ∈ ord_iso(A,r,B,s)⟧ ⟹ part_ord(A,r)"
apply (simp add: part_ord_def irrefl_def trans_on_def ord_iso_def)
apply (fast intro: bij_is_fun [THEN apply_type])
done

lemma linear_ord_iso:
"⟦linear(B,s);  f ∈ ord_iso(A,r,B,s)⟧ ⟹ linear(A,r)"
apply (simp add: linear_def ord_iso_def, safe)
apply (drule_tac x1 = "f`x" and x = "f`y" in bspec [THEN bspec])
apply (safe elim!: bij_is_fun [THEN apply_type])
apply (drule_tac t = "(`) (converse (f))" in subst_context)
done

lemma wf_on_ord_iso:
"⟦wf[B](s);  f ∈ ord_iso(A,r,B,s)⟧ ⟹ wf[A](r)"
apply (simp add: wf_on_def wf_def ord_iso_def, safe)
apply (drule_tac x = "{f`z. z ∈ Z ∩ A}" in spec)
apply (safe intro!: equalityI)
apply (blast dest!: equalityD1 intro: bij_is_fun [THEN apply_type])+
done

lemma well_ord_ord_iso:
"⟦well_ord(B,s);  f ∈ ord_iso(A,r,B,s)⟧ ⟹ well_ord(A,r)"
unfolding well_ord_def tot_ord_def
apply (fast elim!: part_ord_ord_iso linear_ord_iso wf_on_ord_iso)
done

subsection‹Main results of Kunen, Chapter 1 section 6›

(*Inductive argument for Kunen's Lemma 6.1, etc.
Simple proof from Halmos, page 72*)
lemma well_ord_iso_subset_lemma:
"⟦well_ord(A,r);  f ∈ ord_iso(A,r, A',r);  A'<= A;  y ∈ A⟧
⟹ ¬ <f`y, y>: r"
apply (elim conjE CollectE)
apply (rule_tac a=y in wf_on_induct, assumption+)
apply (blast dest: bij_is_fun [THEN apply_type])
done

(*Kunen's Lemma 6.1 ∈ there's no order-isomorphism to an initial segment
of a well-ordering*)
lemma well_ord_iso_predE:
"⟦well_ord(A,r);  f ∈ ord_iso(A, r, pred(A,x,r), r);  x ∈ A⟧ ⟹ P"
apply (insert well_ord_iso_subset_lemma [of A r f "pred(A,x,r)" x])
(*Now we know  f`x < x *)
apply (drule ord_iso_is_bij [THEN bij_is_fun, THEN apply_type], assumption)
(*Now we also know @{term"f`x ∈ pred(A,x,r)"}: contradiction! *)
done

(*Simple consequence of Lemma 6.1*)
lemma well_ord_iso_pred_eq:
"⟦well_ord(A,r);  f ∈ ord_iso(pred(A,a,r), r, pred(A,c,r), r);
a ∈ A;  c ∈ A⟧ ⟹ a=c"
apply (frule well_ord_is_trans_on)
apply (frule well_ord_is_linear)
apply (erule_tac x=a and y=c in linearE, assumption+)
apply (drule ord_iso_sym)
(*two symmetric cases*)
apply (auto elim!: well_ord_subset [OF _ pred_subset, THEN well_ord_iso_predE]
intro!: predI
done

(*Does not assume r is a wellordering!*)
lemma ord_iso_image_pred:
"⟦f ∈ ord_iso(A,r,B,s);  a ∈ A⟧ ⟹ f `` pred(A,a,r) = pred(B, f`a, s)"
unfolding ord_iso_def pred_def
apply (erule CollectE)
apply (simp (no_asm_simp) add: image_fun [OF bij_is_fun Collect_subset])
apply (rule equalityI)
apply (safe elim!: bij_is_fun [THEN apply_type])
apply (rule RepFun_eqI)
apply (blast intro!: right_inverse_bij [symmetric])
apply (auto simp add: right_inverse_bij  bij_is_fun [THEN apply_funtype])
done

lemma ord_iso_restrict_image:
"⟦f ∈ ord_iso(A,r,B,s);  C<=A⟧
⟹ restrict(f,C) ∈ ord_iso(C, r, f``C, s)"
apply (blast intro: bij_is_inj restrict_bij)
done

(*But in use, A and B may themselves be initial segments.  Then use
trans_pred_pred_eq to simplify the pred(pred...) terms.  See just below.*)
lemma ord_iso_restrict_pred:
"⟦f ∈ ord_iso(A,r,B,s);   a ∈ A⟧
⟹ restrict(f, pred(A,a,r)) ∈ ord_iso(pred(A,a,r), r, pred(B, f`a, s), s)"
apply (blast intro: ord_iso_restrict_image elim: predE)
done

(*Tricky; a lot of forward proof!*)
lemma well_ord_iso_preserving:
"⟦well_ord(A,r);  well_ord(B,s);  ⟨a,c⟩: r;
f ∈ ord_iso(pred(A,a,r), r, pred(B,b,s), s);
g ∈ ord_iso(pred(A,c,r), r, pred(B,d,s), s);
a ∈ A;  c ∈ A;  b ∈ B;  d ∈ B⟧ ⟹ ⟨b,d⟩: s"
apply (frule ord_iso_is_bij [THEN bij_is_fun, THEN apply_type], (erule asm_rl predI predE)+)
apply (subgoal_tac "b = g`a")
apply (simp (no_asm_simp))
apply (rule well_ord_iso_pred_eq, auto)
apply (frule ord_iso_restrict_pred, (erule asm_rl predI)+)
apply (erule ord_iso_sym [THEN ord_iso_trans], assumption)
done

(*See Halmos, page 72*)
lemma well_ord_iso_unique_lemma:
"⟦well_ord(A,r);
f ∈ ord_iso(A,r, B,s);  g ∈ ord_iso(A,r, B,s);  y ∈ A⟧
⟹ ¬ <g`y, f`y> ∈ s"
apply (frule well_ord_iso_subset_lemma)
apply (rule_tac f = "converse (f) " and g = g in ord_iso_trans)
apply auto
apply (blast intro: ord_iso_sym)
apply (frule ord_iso_is_bij [of f])
apply (frule ord_iso_is_bij [of g])
apply (frule ord_iso_converse)
apply (blast intro!: bij_converse_bij
intro: bij_is_fun apply_funtype)+
apply (erule notE)
apply (simp add: left_inverse_bij bij_is_fun comp_fun_apply [of _ A B])
done

(*Kunen's Lemma 6.2: Order-isomorphisms between well-orderings are unique*)
lemma well_ord_iso_unique: "⟦well_ord(A,r);
f ∈ ord_iso(A,r, B,s);  g ∈ ord_iso(A,r, B,s)⟧ ⟹ f = g"
apply (rule fun_extension)
apply (erule ord_iso_is_bij [THEN bij_is_fun])+
apply (subgoal_tac "f`x ∈ B ∧ g`x ∈ B ∧ linear(B,s)")
apply (blast dest: well_ord_iso_unique_lemma)
apply (blast intro: ord_iso_is_bij bij_is_fun apply_funtype
well_ord_is_linear well_ord_ord_iso ord_iso_sym)
done

subsection‹Towards Kunen's Theorem 6.3: Linearity of the Similarity Relation›

lemma ord_iso_map_subset: "ord_iso_map(A,r,B,s) ⊆ A*B"
by (unfold ord_iso_map_def, blast)

lemma domain_ord_iso_map: "domain(ord_iso_map(A,r,B,s)) ⊆ A"
by (unfold ord_iso_map_def, blast)

lemma range_ord_iso_map: "range(ord_iso_map(A,r,B,s)) ⊆ B"
by (unfold ord_iso_map_def, blast)

lemma converse_ord_iso_map:
"converse(ord_iso_map(A,r,B,s)) = ord_iso_map(B,s,A,r)"
unfolding ord_iso_map_def
apply (blast intro: ord_iso_sym)
done

lemma function_ord_iso_map:
"well_ord(B,s) ⟹ function(ord_iso_map(A,r,B,s))"
unfolding ord_iso_map_def function_def
apply (blast intro: well_ord_iso_pred_eq ord_iso_sym ord_iso_trans)
done

lemma ord_iso_map_fun: "well_ord(B,s) ⟹ ord_iso_map(A,r,B,s)
∈ domain(ord_iso_map(A,r,B,s)) -> range(ord_iso_map(A,r,B,s))"
ord_iso_map_subset [THEN domain_times_range])

lemma ord_iso_map_mono_map:
"⟦well_ord(A,r);  well_ord(B,s)⟧
⟹ ord_iso_map(A,r,B,s)
∈ mono_map(domain(ord_iso_map(A,r,B,s)), r,
range(ord_iso_map(A,r,B,s)), s)"
unfolding mono_map_def
apply safe
apply (subgoal_tac "x ∈ A ∧ ya:A ∧ y ∈ B ∧ yb:B")
apply (simp add: apply_equality [OF _  ord_iso_map_fun])
unfolding ord_iso_map_def
apply (blast intro: well_ord_iso_preserving, blast)
done

lemma ord_iso_map_ord_iso:
"⟦well_ord(A,r);  well_ord(B,s)⟧ ⟹ ord_iso_map(A,r,B,s)
∈ ord_iso(domain(ord_iso_map(A,r,B,s)), r,
range(ord_iso_map(A,r,B,s)), s)"
apply (rule well_ord_mono_ord_isoI)
prefer 4
apply (rule converse_ord_iso_map [THEN subst])
ord_iso_map_subset [THEN converse_converse])
apply (blast intro!: domain_ord_iso_map range_ord_iso_map
intro: well_ord_subset ord_iso_map_mono_map)+
done

(*One way of saying that domain(ord_iso_map(A,r,B,s)) is downwards-closed*)
lemma domain_ord_iso_map_subset:
"⟦well_ord(A,r);  well_ord(B,s);
a ∈ A;  a ∉ domain(ord_iso_map(A,r,B,s))⟧
⟹  domain(ord_iso_map(A,r,B,s)) ⊆ pred(A, a, r)"
unfolding ord_iso_map_def
apply (safe intro!: predI)
(*Case analysis on  xa vs a in r *)
apply (simp (no_asm_simp))
apply (frule_tac A = A in well_ord_is_linear)
apply (rename_tac b y f)
apply (erule_tac x=b and y=a in linearE, assumption+)
(*Trivial case: b=a*)
apply clarify
apply blast
(*Harder case: ⟨a, xa⟩: r*)
apply (frule ord_iso_is_bij [THEN bij_is_fun, THEN apply_type],
(erule asm_rl predI predE)+)
apply (frule ord_iso_restrict_pred)
apply (simp split: split_if_asm
add: well_ord_is_trans_on trans_pred_pred_eq domain_UN domain_Union, blast)
done

(*For the 4-way case analysis in the main result*)
lemma domain_ord_iso_map_cases:
"⟦well_ord(A,r);  well_ord(B,s)⟧
⟹ domain(ord_iso_map(A,r,B,s)) = A |
(∃x∈A. domain(ord_iso_map(A,r,B,s)) = pred(A,x,r))"
apply (frule well_ord_is_wf)
unfolding wf_on_def wf_def
apply (drule_tac x = "A-domain (ord_iso_map (A,r,B,s))" in spec)
apply safe
(*The first case: the domain equals A*)
apply (rule domain_ord_iso_map [THEN equalityI])
apply (erule Diff_eq_0_iff [THEN iffD1])
(*The other case: the domain equals an initial segment*)
apply (blast del: domainI subsetI
elim!: predE
intro!: domain_ord_iso_map_subset
intro: subsetI)+
done

(*As above, by duality*)
lemma range_ord_iso_map_cases:
"⟦well_ord(A,r);  well_ord(B,s)⟧
⟹ range(ord_iso_map(A,r,B,s)) = B |
(∃y∈B. range(ord_iso_map(A,r,B,s)) = pred(B,y,s))"
apply (rule converse_ord_iso_map [THEN subst])
done

text‹Kunen's Theorem 6.3: Fundamental Theorem for Well-Ordered Sets›
theorem well_ord_trichotomy:
"⟦well_ord(A,r);  well_ord(B,s)⟧
⟹ ord_iso_map(A,r,B,s) ∈ ord_iso(A, r, B, s) |
(∃x∈A. ord_iso_map(A,r,B,s) ∈ ord_iso(pred(A,x,r), r, B, s)) |
(∃y∈B. ord_iso_map(A,r,B,s) ∈ ord_iso(A, r, pred(B,y,s), s))"
apply (frule_tac B = B in domain_ord_iso_map_cases, assumption)
apply (frule_tac B = B in range_ord_iso_map_cases, assumption)
apply (drule ord_iso_map_ord_iso, assumption)
apply (elim disjE bexE)
apply (rule wf_on_not_refl [THEN notE])
apply (erule well_ord_is_wf)
apply assumption
apply (subgoal_tac "⟨x,y⟩: ord_iso_map (A,r,B,s) ")
apply (drule rangeI)
apply (unfold ord_iso_map_def, blast)
done

subsection‹Miscellaneous Results by Krzysztof Grabczewski›

(** Properties of converse(r) **)

lemma irrefl_converse: "irrefl(A,r) ⟹ irrefl(A,converse(r))"
by (unfold irrefl_def, blast)

lemma trans_on_converse: "trans[A](r) ⟹ trans[A](converse(r))"
by (unfold trans_on_def, blast)

lemma part_ord_converse: "part_ord(A,r) ⟹ part_ord(A,converse(r))"
unfolding part_ord_def
apply (blast intro!: irrefl_converse trans_on_converse)
done

lemma linear_converse: "linear(A,r) ⟹ linear(A,converse(r))"
by (unfold linear_def, blast)

lemma tot_ord_converse: "tot_ord(A,r) ⟹ tot_ord(A,converse(r))"
unfolding tot_ord_def
apply (blast intro!: part_ord_converse linear_converse)
done

(** By Krzysztof Grabczewski.
Lemmas involving the first element of a well ordered set **)

lemma first_is_elem: "first(b,B,r) ⟹ b ∈ B"
by (unfold first_def, blast)

lemma well_ord_imp_ex1_first:
"⟦well_ord(A,r); B<=A; B≠0⟧ ⟹ (∃!b. first(b,B,r))"
unfolding well_ord_def wf_on_def wf_def first_def
apply (elim conjE allE disjE, blast)
apply (erule bexE)
apply (rule_tac a = x in ex1I, auto)
apply (unfold tot_ord_def linear_def, blast)
done

lemma the_first_in:
"⟦well_ord(A,r); B<=A; B≠0⟧ ⟹ (THE b. first(b,B,r)) ∈ B"
apply (drule well_ord_imp_ex1_first, assumption+)
apply (rule first_is_elem)
apply (erule theI)
done

subsection ‹Lemmas for the Reflexive Orders›

lemma subset_vimage_vimage_iff:
"⟦Preorder(r); A ⊆ field(r); B ⊆ field(r)⟧ ⟹
r -`` A ⊆ r -`` B ⟷ (∀a∈A. ∃b∈B. ⟨a, b⟩ ∈ r)"
apply (auto simp: subset_def preorder_on_def refl_def vimage_def image_def)
apply blast
unfolding trans_on_def
apply (erule_tac P = "(λx. ∀y∈field(r).
∀z∈field(r). ⟨x, y⟩ ∈ r ⟶ ⟨y, z⟩ ∈ r ⟶ ⟨x, z⟩ ∈ r)" for r in rev_ballE)
(* instance obtained from proof term generated by best *)
apply best
apply blast
done

lemma subset_vimage1_vimage1_iff:
"⟦Preorder(r); a ∈ field(r); b ∈ field(r)⟧ ⟹
r -`` {a} ⊆ r -`` {b} ⟷ ⟨a, b⟩ ∈ r"

lemma Refl_antisym_eq_Image1_Image1_iff:
"⟦refl(field(r), r); antisym(r); a ∈ field(r); b ∈ field(r)⟧ ⟹
r `` {a} = r `` {b} ⟷ a = b"
apply rule
apply (frule equality_iffD)
apply (drule equality_iffD)
apply best
done

lemma Partial_order_eq_Image1_Image1_iff:
"⟦Partial_order(r); a ∈ field(r); b ∈ field(r)⟧ ⟹
r `` {a} = r `` {b} ⟷ a = b"
Refl_antisym_eq_Image1_Image1_iff)

lemma Refl_antisym_eq_vimage1_vimage1_iff:
"⟦refl(field(r), r); antisym(r); a ∈ field(r); b ∈ field(r)⟧ ⟹
r -`` {a} = r -`` {b} ⟷ a = b"
apply rule
apply (frule equality_iffD)
apply (drule equality_iffD)