# Theory OrderType

```(*  Title:      ZF/OrderType.thy
Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright   1994  University of Cambridge
*)

section‹Order Types and Ordinal Arithmetic›

theory OrderType imports OrderArith OrdQuant Nat begin

text‹The order type of a well-ordering is the least ordinal isomorphic to it.
Ordinal arithmetic is traditionally defined in terms of order types, as it is
here.  But a definition by transfinite recursion would be much simpler!›

definition
ordermap  :: "[i,i]⇒i"  where
"ordermap(A,r) ≡ λx∈A. wfrec[A](r, x, λx f. f `` pred(A,x,r))"

definition
ordertype :: "[i,i]⇒i"  where
"ordertype(A,r) ≡ ordermap(A,r)``A"

definition
(*alternative definition of ordinal numbers*)
Ord_alt   :: "i ⇒ o"  where
"Ord_alt(X) ≡ well_ord(X, Memrel(X)) ∧ (∀u∈X. u=pred(X, u, Memrel(X)))"

definition
(*coercion to ordinal: if not, just 0*)
ordify    :: "i⇒i"  where
"ordify(x) ≡ if Ord(x) then x else 0"

definition
(*ordinal multiplication*)
omult      :: "[i,i]⇒i"           (infixl ‹**› 70)  where
"i ** j ≡ ordertype(j*i, rmult(j,Memrel(j),i,Memrel(i)))"

definition
raw_oadd   :: "[i,i]⇒i"  where

definition
oadd      :: "[i,i]⇒i"           (infixl ‹++› 65)  where
"i ++ j ≡ raw_oadd(ordify(i),ordify(j))"

definition
(*ordinal subtraction*)
odiff      :: "[i,i]⇒i"           (infixl ‹--› 65)  where
"i -- j ≡ ordertype(i-j, Memrel(i))"

subsection‹Proofs needing the combination of Ordinal.thy and Order.thy›

lemma le_well_ord_Memrel: "j ≤ i ⟹ well_ord(j, Memrel(i))"
apply (rule well_ordI)
apply (rule wf_Memrel [THEN wf_imp_wf_on])
apply (simp add: ltD lt_Ord linear_def
ltI [THEN lt_trans2 [of _ j i]])
apply (intro ballI Ord_linear)
apply (blast intro: Ord_in_Ord lt_Ord)+
done

(*"Ord(i) ⟹ well_ord(i, Memrel(i))"*)
lemmas well_ord_Memrel = le_refl [THEN le_well_ord_Memrel]

(*Kunen's Theorem 7.3 (i), page 16;  see also Ordinal/Ord_in_Ord
The smaller ordinal is an initial segment of the larger *)
lemma lt_pred_Memrel:
"j<i ⟹ pred(i, j, Memrel(i)) = j"
apply (simp add: pred_def lt_def)
apply (blast intro: Ord_trans)
done

lemma pred_Memrel:
"x ∈ A ⟹ pred(A, x, Memrel(A)) = A ∩ x"
by (unfold pred_def Memrel_def, blast)

lemma Ord_iso_implies_eq_lemma:
"⟦j<i;  f ∈ ord_iso(i,Memrel(i),j,Memrel(j))⟧ ⟹ R"
apply (frule lt_pred_Memrel)
apply (erule ltE)
apply (rule well_ord_Memrel [THEN well_ord_iso_predE, of i f j], auto)
unfolding ord_iso_def
(*Combining the two simplifications causes looping*)
apply (simp (no_asm_simp))
apply (blast intro: bij_is_fun [THEN apply_type] Ord_trans)
done

(*Kunen's Theorem 7.3 (ii), page 16.  Isomorphic ordinals are equal*)
lemma Ord_iso_implies_eq:
"⟦Ord(i);  Ord(j);  f ∈ ord_iso(i,Memrel(i),j,Memrel(j))⟧
⟹ i=j"
apply (rule_tac i = i and j = j in Ord_linear_lt)
apply (blast intro: ord_iso_sym Ord_iso_implies_eq_lemma)+
done

subsection‹Ordermap and ordertype›

lemma ordermap_type:
"ordermap(A,r) ∈ A -> ordertype(A,r)"
unfolding ordermap_def ordertype_def
apply (rule lam_type)
apply (rule lamI [THEN imageI], assumption+)
done

subsubsection‹Unfolding of ordermap›

(*Useful for cardinality reasoning; see CardinalArith.ML*)
lemma ordermap_eq_image:
"⟦wf[A](r);  x ∈ A⟧
⟹ ordermap(A,r) ` x = ordermap(A,r) `` pred(A,x,r)"
unfolding ordermap_def pred_def
apply (simp (no_asm_simp))
apply (erule wfrec_on [THEN trans], assumption)
apply (simp (no_asm_simp) add: subset_iff image_lam vimage_singleton_iff)
done

(*Useful for rewriting PROVIDED pred is not unfolded until later!*)
lemma ordermap_pred_unfold:
"⟦wf[A](r);  x ∈ A⟧
⟹ ordermap(A,r) ` x = {ordermap(A,r)`y . y ∈ pred(A,x,r)}"
by (simp add: ordermap_eq_image pred_subset ordermap_type [THEN image_fun])

(*pred-unfolded version.  NOT suitable for rewriting -- loops!*)
lemmas ordermap_unfold = ordermap_pred_unfold [simplified pred_def]

(*The theorem above is

⟦wf[A](r); x ∈ A⟧
⟹ ordermap(A,r) ` x = {ordermap(A,r) ` y . y: {y ∈ A . ⟨y,x⟩ ∈ r}}

NOTE: the definition of ordermap used here delivers ordinals only if r is
transitive.  If r is the predecessor relation on the naturals then
ordermap(nat,predr) ` n equals {n-1} and not n.  A more complicated definition,
like

ordermap(A,r) ` x = Union{succ(ordermap(A,r) ` y) . y: {y ∈ A . ⟨y,x⟩ ∈ r}},

might eliminate the need for r to be transitive.
*)

subsubsection‹Showing that ordermap, ordertype yield ordinals›

lemma Ord_ordermap:
"⟦well_ord(A,r);  x ∈ A⟧ ⟹ Ord(ordermap(A,r) ` x)"
apply (unfold well_ord_def tot_ord_def part_ord_def, safe)
apply (rule_tac a=x in wf_on_induct, assumption+)
apply (simp (no_asm_simp) add: ordermap_pred_unfold)
apply (rule OrdI [OF _ Ord_is_Transset])
unfolding pred_def Transset_def
apply (blast intro: trans_onD
dest!: ordermap_unfold [THEN equalityD1])+
done

lemma Ord_ordertype:
"well_ord(A,r) ⟹ Ord(ordertype(A,r))"
unfolding ordertype_def
apply (subst image_fun [OF ordermap_type subset_refl])
apply (rule OrdI [OF _ Ord_is_Transset])
prefer 2 apply (blast intro: Ord_ordermap)
unfolding Transset_def well_ord_def
apply (blast intro: trans_onD
dest!: ordermap_unfold [THEN equalityD1])
done

subsubsection‹ordermap preserves the orderings in both directions›

lemma ordermap_mono:
"⟦⟨w,x⟩: r;  wf[A](r);  w ∈ A; x ∈ A⟧
⟹ ordermap(A,r)`w ∈ ordermap(A,r)`x"
apply (erule_tac x1 = x in ordermap_unfold [THEN ssubst], assumption, blast)
done

(*linearity of r is crucial here*)
lemma converse_ordermap_mono:
"⟦ordermap(A,r)`w ∈ ordermap(A,r)`x;  well_ord(A,r); w ∈ A; x ∈ A⟧
⟹ ⟨w,x⟩: r"
apply (unfold well_ord_def tot_ord_def, safe)
apply (erule_tac x=w and y=x in linearE, assumption+)
apply (blast elim!: mem_not_refl [THEN notE])
apply (blast dest: ordermap_mono intro: mem_asym)
done

lemma ordermap_surj: "ordermap(A, r) ∈ surj(A, ordertype(A, r))"
unfolding ordertype_def
by (rule surj_image) (rule ordermap_type)

lemma ordermap_bij:
"well_ord(A,r) ⟹ ordermap(A,r) ∈ bij(A, ordertype(A,r))"
unfolding well_ord_def tot_ord_def bij_def inj_def
apply (force intro!: ordermap_type ordermap_surj
elim: linearE dest: ordermap_mono
done

subsubsection‹Isomorphisms involving ordertype›

lemma ordertype_ord_iso:
"well_ord(A,r)
⟹ ordermap(A,r) ∈ ord_iso(A,r, ordertype(A,r), Memrel(ordertype(A,r)))"
unfolding ord_iso_def
apply (safe elim!: well_ord_is_wf
intro!: ordermap_type [THEN apply_type] ordermap_mono ordermap_bij)
apply (blast dest!: converse_ordermap_mono)
done

lemma ordertype_eq:
"⟦f ∈ ord_iso(A,r,B,s);  well_ord(B,s)⟧
⟹ ordertype(A,r) = ordertype(B,s)"
apply (frule well_ord_ord_iso, assumption)
apply (rule Ord_iso_implies_eq, (erule Ord_ordertype)+)
apply (blast intro: ord_iso_trans ord_iso_sym ordertype_ord_iso)
done

lemma ordertype_eq_imp_ord_iso:
"⟦ordertype(A,r) = ordertype(B,s); well_ord(A,r);  well_ord(B,s)⟧
⟹ ∃f. f ∈ ord_iso(A,r,B,s)"
apply (rule exI)
apply (rule ordertype_ord_iso [THEN ord_iso_trans], assumption)
apply (erule ssubst)
apply (erule ordertype_ord_iso [THEN ord_iso_sym])
done

subsubsection‹Basic equalities for ordertype›

(*Ordertype of Memrel*)
lemma le_ordertype_Memrel: "j ≤ i ⟹ ordertype(j,Memrel(i)) = j"
apply (rule Ord_iso_implies_eq [symmetric])
apply (erule ltE, assumption)
apply (blast intro: le_well_ord_Memrel Ord_ordertype)
apply (rule ord_iso_trans)
apply (erule_tac [2] le_well_ord_Memrel [THEN ordertype_ord_iso])
apply (rule id_bij [THEN ord_isoI])
apply (simp (no_asm_simp))
apply (fast elim: ltE Ord_in_Ord Ord_trans)
done

(*"Ord(i) ⟹ ordertype(i, Memrel(i)) = i"*)
lemmas ordertype_Memrel = le_refl [THEN le_ordertype_Memrel]

lemma ordertype_0 [simp]: "ordertype(0,r) = 0"
apply (rule id_bij [THEN ord_isoI, THEN ordertype_eq, THEN trans])
apply (erule emptyE)
apply (rule well_ord_0)
apply (rule Ord_0 [THEN ordertype_Memrel])
done

(*Ordertype of rvimage:  ⟦f ∈ bij(A,B);  well_ord(B,s)⟧ ⟹
ordertype(A, rvimage(A,f,s)) = ordertype(B,s) *)
lemmas bij_ordertype_vimage = ord_iso_rvimage [THEN ordertype_eq]

subsubsection‹A fundamental unfolding law for ordertype.›

(*Ordermap returns the same result if applied to an initial segment*)
lemma ordermap_pred_eq_ordermap:
"⟦well_ord(A,r);  y ∈ A;  z ∈ pred(A,y,r)⟧
⟹ ordermap(pred(A,y,r), r) ` z = ordermap(A, r) ` z"
apply (frule wf_on_subset_A [OF well_ord_is_wf pred_subset])
apply (rule_tac a=z in wf_on_induct, assumption+)
apply (safe elim!: predE)
apply (simp (no_asm_simp) add: ordermap_pred_unfold well_ord_is_wf pred_iff)
(*combining these two simplifications LOOPS! *)
apply (simp (no_asm_simp) add: pred_pred_eq)
apply (simp add: pred_def)
apply (rule RepFun_cong [OF _ refl])
apply (drule well_ord_is_trans_on)
apply (fast elim!: trans_onD)
done

lemma ordertype_unfold:
"ordertype(A,r) = {ordermap(A,r)`y . y ∈ A}"
unfolding ordertype_def
apply (rule image_fun [OF ordermap_type subset_refl])
done

text‹Theorems by Krzysztof Grabczewski; proofs simplified by lcp›

lemma ordertype_pred_subset: "⟦well_ord(A,r);  x ∈ A⟧ ⟹
ordertype(pred(A,x,r),r) ⊆ ordertype(A,r)"
apply (simp add: ordertype_unfold well_ord_subset [OF _ pred_subset])
apply (fast intro: ordermap_pred_eq_ordermap elim: predE)
done

lemma ordertype_pred_lt:
"⟦well_ord(A,r);  x ∈ A⟧
⟹ ordertype(pred(A,x,r),r) < ordertype(A,r)"
apply (rule ordertype_pred_subset [THEN subset_imp_le, THEN leE])
apply (simp_all add: Ord_ordertype well_ord_subset [OF _ pred_subset])
apply (erule sym [THEN ordertype_eq_imp_ord_iso, THEN exE])
apply (erule_tac [3] well_ord_iso_predE)
apply (simp_all add: well_ord_subset [OF _ pred_subset])
done

(*May rewrite with this -- provided no rules are supplied for proving that
well_ord(pred(A,x,r), r) *)
lemma ordertype_pred_unfold:
"well_ord(A,r)
⟹ ordertype(A,r) = {ordertype(pred(A,x,r),r). x ∈ A}"
apply (rule equalityI)
apply (safe intro!: ordertype_pred_lt [THEN ltD])
apply (auto simp add: ordertype_def well_ord_is_wf [THEN ordermap_eq_image]
ordermap_type [THEN image_fun]
ordermap_pred_eq_ordermap pred_subset)
done

subsection‹Alternative definition of ordinal›

(*proof by Krzysztof Grabczewski*)
lemma Ord_is_Ord_alt: "Ord(i) ⟹ Ord_alt(i)"
unfolding Ord_alt_def
apply (rule conjI)
apply (erule well_ord_Memrel)
apply (unfold Ord_def Transset_def pred_def Memrel_def, blast)
done

(*proof by lcp*)
lemma Ord_alt_is_Ord:
"Ord_alt(i) ⟹ Ord(i)"
apply (unfold Ord_alt_def Ord_def Transset_def well_ord_def
tot_ord_def part_ord_def trans_on_def)
apply (simp add: pred_Memrel)
apply (blast elim!: equalityE)
done

subsubsection‹Order Type calculations for radd›

lemma bij_sum_0: "(λz∈A+0. case(λx. x, λy. y, z)) ∈ bij(A+0, A)"
apply (rule_tac d = Inl in lam_bijective, safe)
apply (simp_all (no_asm_simp))
done

lemma ordertype_sum_0_eq:
"well_ord(A,r) ⟹ ordertype(A+0, radd(A,r,0,s)) = ordertype(A,r)"
apply (rule bij_sum_0 [THEN ord_isoI, THEN ordertype_eq])
prefer 2 apply assumption
apply force
done

lemma bij_0_sum: "(λz∈0+A. case(λx. x, λy. y, z)) ∈ bij(0+A, A)"
apply (rule_tac d = Inr in lam_bijective, safe)
apply (simp_all (no_asm_simp))
done

lemma ordertype_0_sum_eq:
"well_ord(A,r) ⟹ ordertype(0+A, radd(0,s,A,r)) = ordertype(A,r)"
apply (rule bij_0_sum [THEN ord_isoI, THEN ordertype_eq])
prefer 2 apply assumption
apply force
done

text‹Initial segments of radd.  Statements by Grabczewski›

(*In fact, pred(A+B, Inl(a), radd(A,r,B,s)) = pred(A,a,r)+0 *)
lemma pred_Inl_bij:
"a ∈ A ⟹ (λx∈pred(A,a,r). Inl(x))
∈ bij(pred(A,a,r), pred(A+B, Inl(a), radd(A,r,B,s)))"
unfolding pred_def
apply (rule_tac d = "case (λx. x, λy. y) " in lam_bijective)
apply auto
done

lemma ordertype_pred_Inl_eq:
"⟦a ∈ A;  well_ord(A,r)⟧
ordertype(pred(A,a,r), r)"
apply (rule pred_Inl_bij [THEN ord_isoI, THEN ord_iso_sym, THEN ordertype_eq])
apply (simp_all add: well_ord_subset [OF _ pred_subset])
apply (simp add: pred_def)
done

lemma pred_Inr_bij:
"b ∈ B ⟹
id(A+pred(B,b,s))
∈ bij(A+pred(B,b,s), pred(A+B, Inr(b), radd(A,r,B,s)))"
unfolding pred_def id_def
apply (rule_tac d = "λz. z" in lam_bijective, auto)
done

lemma ordertype_pred_Inr_eq:
"⟦b ∈ B;  well_ord(A,r);  well_ord(B,s)⟧
apply (rule pred_Inr_bij [THEN ord_isoI, THEN ord_iso_sym, THEN ordertype_eq])
prefer 2 apply (force simp add: pred_def id_def, assumption)
apply (blast intro: well_ord_radd well_ord_subset [OF _ pred_subset])
done

subsubsection‹ordify: trivial coercion to an ordinal›

lemma Ord_ordify [iff, TC]: "Ord(ordify(x))"
by (simp add: ordify_def)

(*Collapsing*)
lemma ordify_idem [simp]: "ordify(ordify(x)) = ordify(x)"
by (simp add: ordify_def)

subsubsection‹Basic laws for ordinal addition›

well_ord_Memrel)

lemma Ord_oadd [iff,TC]: "Ord(i++j)"

text‹Ordinal addition with zero›

lemma raw_oadd_0: "Ord(i) ⟹ raw_oadd(i,0) = i"
ordertype_Memrel well_ord_Memrel)

lemma oadd_0 [simp]: "Ord(i) ⟹ i++0 = i"
done

lemma raw_oadd_0_left: "Ord(i) ⟹ raw_oadd(0,i) = i"
by (simp add: raw_oadd_def ordify_def ordertype_0_sum_eq ordertype_Memrel
well_ord_Memrel)

lemma oadd_0_left [simp]: "Ord(i) ⟹ 0++i = i"

"i++j = (if Ord(i) then (if Ord(j) then raw_oadd(i,j) else i)
else (if Ord(j) then j else 0))"

(*** Further properties of ordinal addition.  Statements by Grabczewski,
proofs by lcp. ***)

(*Surely also provable by transfinite induction on j?*)
lemma lt_oadd1: "k<i ⟹ k < i++j"
apply (rule ltE, assumption)
apply (rule ltI)
apply (force simp add: ordertype_pred_unfold well_ord_radd well_ord_Memrel
ordertype_pred_Inl_eq lt_pred_Memrel leI [THEN le_ordertype_Memrel])
apply (blast intro: Ord_ordertype well_ord_radd well_ord_Memrel)
done

(*Thus also we obtain the rule  @{term"i++j = k ⟹ i ≤ k"} *)
lemma oadd_le_self: "Ord(i) ⟹ i ≤ i++j"
apply (rule all_lt_imp_le)
done

text‹Various other results›

lemma id_ord_iso_Memrel: "A<=B ⟹ id(A) ∈ ord_iso(A, Memrel(A), A, Memrel(B))"
apply (rule id_bij [THEN ord_isoI])
apply (simp (no_asm_simp))
apply blast
done

lemma subset_ord_iso_Memrel:
"⟦f ∈ ord_iso(A,Memrel(B),C,r); A<=B⟧ ⟹ f ∈ ord_iso(A,Memrel(A),C,r)"
apply (frule ord_iso_is_bij [THEN bij_is_fun, THEN fun_is_rel])
apply (frule ord_iso_trans [OF id_ord_iso_Memrel], assumption)
apply (simp add: right_comp_id)
done

lemma restrict_ord_iso:
"⟦f ∈ ord_iso(i, Memrel(i), Order.pred(A,a,r), r);  a ∈ A; j < i;
trans[A](r)⟧
⟹ restrict(f,j) ∈ ord_iso(j, Memrel(j), Order.pred(A,f`j,r), r)"
apply (frule ltD)
apply (frule ord_iso_is_bij [THEN bij_is_fun, THEN apply_type], assumption)
apply (frule ord_iso_restrict_pred, assumption)
apply (simp add: pred_iff trans_pred_pred_eq lt_pred_Memrel)
apply (blast intro!: subset_ord_iso_Memrel le_imp_subset [OF leI])
done

lemma restrict_ord_iso2:
"⟦f ∈ ord_iso(Order.pred(A,a,r), r, i, Memrel(i));  a ∈ A;
j < i; trans[A](r)⟧
⟹ converse(restrict(converse(f), j))
∈ ord_iso(Order.pred(A, converse(f)`j, r), r, j, Memrel(j))"
by (blast intro: restrict_ord_iso ord_iso_sym ltI)

lemma ordertype_sum_Memrel:
"⟦well_ord(A,r);  k<j⟧
⟹ ordertype(A+k, radd(A, r, k, Memrel(j))) =
ordertype(A+k, radd(A, r, k, Memrel(k)))"
apply (erule ltE)
apply (rule ord_iso_refl [THEN sum_ord_iso_cong, THEN ordertype_eq])
apply (erule OrdmemD [THEN id_ord_iso_Memrel, THEN ord_iso_sym])
done

lemma oadd_lt_mono2: "k<j ⟹ i++k < i++j"
apply (rule ltE, assumption)
apply (rule ordertype_pred_unfold [THEN equalityD2, THEN subsetD, THEN ltI])
apply (rule bexI)
apply (erule_tac [2] InrI)
apply (simp add: ordertype_pred_Inr_eq well_ord_Memrel lt_pred_Memrel
leI [THEN le_ordertype_Memrel] ordertype_sum_Memrel)
done

lemma oadd_lt_cancel2: "⟦i++j < i++k;  Ord(j)⟧ ⟹ j<k"
prefer 2
apply (frule_tac i = i and j = j in oadd_le_self)
apply (simp (asm_lr) add: oadd_def ordify_def lt_Ord not_lt_iff_le [THEN iff_sym])
apply (rule Ord_linear_lt, auto)
apply (blast dest: oadd_lt_mono2 elim: lt_irrefl lt_asym)+
done

lemma oadd_lt_iff2: "Ord(j) ⟹ i++j < i++k ⟷ j<k"

lemma oadd_inject: "⟦i++j = i++k;  Ord(j); Ord(k)⟧ ⟹ j=k"
apply (rule Ord_linear_lt, auto)
apply (force dest: oadd_lt_mono2 [of concl: i] simp add: lt_not_refl)+
done

lemma lt_oadd_disj: "k < i++j ⟹ k<i | (∃l∈j. k = i++l )"
split: split_if_asm)
prefer 2
apply (simp add: Ord_in_Ord' [of _ j] lt_def)
apply (erule ltD [THEN RepFunE])
apply (force simp add: ordertype_pred_Inl_eq well_ord_Memrel ltI
lt_pred_Memrel le_ordertype_Memrel leI
ordertype_pred_Inr_eq ordertype_sum_Memrel)
done

subsubsection‹Ordinal addition with successor -- via associativity!›

lemma oadd_assoc: "(i++j)++k = i++(j++k)"
apply (rule ordertype_eq [THEN trans])
apply (rule sum_ord_iso_cong [OF ordertype_ord_iso [THEN ord_iso_sym]
ord_iso_refl])
apply (rule sum_assoc_ord_iso [THEN ordertype_eq, THEN trans])
apply (rule_tac [2] ordertype_eq)
apply (rule_tac [2] sum_ord_iso_cong [OF ord_iso_refl ordertype_ord_iso])
apply (blast intro: Ord_ordertype well_ord_radd well_ord_Memrel)+
done

lemma oadd_unfold: "⟦Ord(i);  Ord(j)⟧ ⟹ i++j = i ∪ (⋃k∈j. {i++k})"
apply (rule subsetI [THEN equalityI])
apply (erule ltI [THEN lt_oadd_disj, THEN disjE])
apply (blast intro: Ord_oadd)
apply (blast elim!: ltE, blast)
done

lemma oadd_1: "Ord(i) ⟹ i++1 = succ(i)"
apply blast
done

lemma oadd_succ [simp]: "Ord(j) ⟹ i++succ(j) = succ(i++j)"
apply (simp add: oadd_1 [of j, symmetric] oadd_1 [of "i++j", symmetric]
done

text‹Ordinal addition with limit ordinals›

"⟦⋀x. x ∈ A ⟹ Ord(j(x));  a ∈ A⟧
⟹ i ++ (⋃x∈A. j(x)) = (⋃x∈A. i++j(x))"
by (blast intro: ltI Ord_UN Ord_oadd lt_oadd1 [THEN ltD]
elim!: ltE dest!: ltI [THEN lt_oadd_disj])

lemma oadd_Limit: "Limit(j) ⟹ i++j = (⋃k∈j. i++k)"
apply (frule Limit_has_0 [THEN ltD])
apply (simp add: Limit_is_Ord [THEN Ord_in_Ord] oadd_UN [symmetric]
Union_eq_UN [symmetric] Limit_Union_eq)
done

lemma oadd_eq_0_iff: "⟦Ord(i); Ord(j)⟧ ⟹ (i ++ j) = 0 ⟷ i=0 ∧ j=0"
apply (erule trans_induct3 [of j])
apply (simp add: Union_empty_iff Limit_def lt_def, blast)
done

lemma oadd_eq_lt_iff: "⟦Ord(i); Ord(j)⟧ ⟹ 0 < (i ++ j) ⟷ 0<i | 0<j"

lemma oadd_LimitI: "⟦Ord(i); Limit(j)⟧ ⟹ Limit(i ++ j)"
apply (frule Limit_has_1 [THEN ltD])
apply (rule increasing_LimitI)
apply (rule Ord_0_lt)
apply (blast intro: Ord_in_Ord [OF Limit_is_Ord])
Limit_is_Ord [of j, THEN Ord_in_Ord], auto)
apply (rule_tac x="succ(y)" in bexI)
apply (simp add: ltI Limit_is_Ord [of j, THEN Ord_in_Ord])
apply (simp add: Limit_def lt_def)
done

text‹Order/monotonicity properties of ordinal addition›

lemma oadd_le_self2: "Ord(i) ⟹ i ≤ j++i"
proof (induct i rule: trans_induct3)
case 0 thus ?case by (simp add: Ord_0_le)
next
case (succ i) thus ?case by (simp add: oadd_succ succ_leI)
next
case (limit l)
hence "l = (⋃x∈l. x)"
by (simp add: Union_eq_UN [symmetric] Limit_Union_eq)
also have "... ≤ (⋃x∈l. j++x)"
by (rule le_implies_UN_le_UN) (rule limit.hyps)
finally have "l ≤ (⋃x∈l. j++x)" .
thus ?case using limit.hyps by (simp add: oadd_Limit)
qed

lemma oadd_le_mono1: "k ≤ j ⟹ k++i ≤ j++i"
apply (frule lt_Ord)
apply (frule le_Ord2)
apply (erule_tac i = i in trans_induct3)
apply (simp (no_asm_simp))
apply (rule le_implies_UN_le_UN, blast)
done

lemma oadd_lt_mono: "⟦i' ≤ i;  j'<j⟧ ⟹ i'++j' < i++j"
by (blast intro: lt_trans1 oadd_le_mono1 oadd_lt_mono2 Ord_succD elim: ltE)

lemma oadd_le_mono: "⟦i' ≤ i;  j' ≤ j⟧ ⟹ i'++j' ≤ i++j"

lemma oadd_le_iff2: "⟦Ord(j); Ord(k)⟧ ⟹ i++j ≤ i++k ⟷ j ≤ k"

lemma oadd_lt_self: "⟦Ord(i);  0<j⟧ ⟹ i < i++j"
apply (rule lt_trans2)
apply (erule le_refl)
apply (simp only: lt_Ord2  oadd_1 [of i, symmetric])
apply (blast intro: succ_leI oadd_le_mono)
done

text‹Every ordinal is exceeded by some limit ordinal.›
lemma Ord_imp_greater_Limit: "Ord(i) ⟹ ∃k. i<k ∧ Limit(k)"
apply (rule_tac x="i ++ nat" in exI)
apply (blast intro: oadd_LimitI  oadd_lt_self  Limit_nat [THEN Limit_has_0])
done

lemma Ord2_imp_greater_Limit: "⟦Ord(i); Ord(j)⟧ ⟹ ∃k. i<k ∧ j<k ∧ Limit(k)"
apply (insert Ord_Un [of i j, THEN Ord_imp_greater_Limit])
apply (simp add: Un_least_lt_iff)
done

subsection‹Ordinal Subtraction›

text‹The difference is \<^term>‹ordertype(j-i, Memrel(j))›.
It's probably simpler to define the difference recursively!›

lemma bij_sum_Diff:
"A<=B ⟹ (λy∈B. if(y ∈ A, Inl(y), Inr(y))) ∈ bij(B, A+(B-A))"
apply (rule_tac d = "case (λx. x, λy. y) " in lam_bijective)
apply (blast intro!: if_type)
apply (fast intro!: case_type)
apply (erule_tac [2] sumE)
apply (simp_all (no_asm_simp))
done

lemma ordertype_sum_Diff:
"i ≤ j ⟹
ordertype(j, Memrel(j))"
apply (safe dest!: le_subset_iff [THEN iffD1])
apply (rule bij_sum_Diff [THEN ord_isoI, THEN ord_iso_sym, THEN ordertype_eq])
apply (erule_tac [3] well_ord_Memrel, assumption)
apply (simp (no_asm_simp))
apply (frule_tac j = y in Ord_in_Ord, assumption)
apply (frule_tac j = x in Ord_in_Ord, assumption)
apply (simp (no_asm_simp) add: Ord_mem_iff_lt lt_Ord not_lt_iff_le)
apply (blast intro: lt_trans2 lt_trans)
done

lemma Ord_odiff [simp,TC]:
"⟦Ord(i);  Ord(j)⟧ ⟹ Ord(i--j)"
unfolding odiff_def
apply (blast intro: Ord_ordertype Diff_subset well_ord_subset well_ord_Memrel)
done

"i ≤ j
apply (safe dest!: le_subset_iff [THEN iffD1])
apply (rule sum_ord_iso_cong [THEN ordertype_eq])
apply (erule id_ord_iso_Memrel)
apply (rule ordertype_ord_iso [THEN ord_iso_sym])
apply (blast intro: well_ord_radd Diff_subset well_ord_subset well_ord_Memrel)+
done

lemma oadd_odiff_inverse: "i ≤ j ⟹ i ++ (j--i) = j"
ordertype_sum_Diff ordertype_Memrel lt_Ord2 [THEN Ord_succD])

(*By oadd_inject, the difference between i and j is unique.  Note that we get
i++j = k  ⟹  j = k--i.  *)
lemma odiff_oadd_inverse: "⟦Ord(i); Ord(j)⟧ ⟹ (i++j) -- i = j"
apply (blast intro: Ord_ordertype Ord_oadd Ord_odiff)+
done

lemma odiff_lt_mono2: "⟦i<j;  k ≤ i⟧ ⟹ i--k < j--k"
apply (rule_tac i = k in oadd_lt_cancel2)
apply (blast intro: le_trans leI, assumption)
apply (simp (no_asm_simp) add: lt_Ord le_Ord2)
done

subsection‹Ordinal Multiplication›

lemma Ord_omult [simp,TC]:
"⟦Ord(i);  Ord(j)⟧ ⟹ Ord(i**j)"
unfolding omult_def
apply (blast intro: Ord_ordertype well_ord_rmult well_ord_Memrel)
done

subsubsection‹A useful unfolding law›

lemma pred_Pair_eq:
"⟦a ∈ A;  b ∈ B⟧ ⟹ pred(A*B, ⟨a,b⟩, rmult(A,r,B,s)) =
pred(A,a,r)*B ∪ ({a} * pred(B,b,s))"
apply (unfold pred_def, blast)
done

lemma ordertype_pred_Pair_eq:
"⟦a ∈ A;  b ∈ B;  well_ord(A,r);  well_ord(B,s)⟧ ⟹
ordertype(pred(A*B, ⟨a,b⟩, rmult(A,r,B,s)), rmult(A,r,B,s)) =
ordertype(pred(A,a,r)*B + pred(B,b,s),
radd(A*B, rmult(A,r,B,s), B, s))"
apply (simp (no_asm_simp) add: pred_Pair_eq)
apply (rule ordertype_eq [symmetric])
apply (rule prod_sum_singleton_ord_iso)
apply (simp_all add: pred_subset well_ord_rmult [THEN well_ord_subset])
apply (blast intro: pred_subset well_ord_rmult [THEN well_ord_subset]
elim!: predE)
done

lemma ordertype_pred_Pair_lemma:
"⟦i'<i;  j'<j⟧
⟹ ordertype(pred(i*j, <i',j'>, rmult(i,Memrel(i),j,Memrel(j))),
rmult(i,Memrel(i),j,Memrel(j))) =
apply (simp add: ordertype_pred_Pair_eq lt_pred_Memrel ltD lt_Ord2
well_ord_Memrel)
apply (rule trans)
apply (rule_tac [2] ordertype_ord_iso
[THEN sum_ord_iso_cong, THEN ordertype_eq])
apply (rule_tac [3] ord_iso_refl)
apply (rule id_bij [THEN ord_isoI, THEN ordertype_eq])
apply (elim SigmaE sumE ltE ssubst)
Ord_ordertype lt_Ord lt_Ord2)
apply (blast intro: Ord_trans)+
done

lemma lt_omult:
"⟦Ord(i);  Ord(j);  k<j**i⟧
⟹ ∃j' i'. k = j**i' ++ j' ∧ j'<j ∧ i'<i"
unfolding omult_def
apply (simp add: ordertype_pred_unfold well_ord_rmult well_ord_Memrel)
apply (safe elim!: ltE)
omult_def [symmetric] Ord_in_Ord' [of _ i] Ord_in_Ord' [of _ j])
apply (blast intro: ltI)
done

"⟦j'<j;  i'<i⟧ ⟹ j**i' ++ j'  <  j**i"
unfolding omult_def
apply (rule ltI)
prefer 2
apply (simp add: Ord_ordertype well_ord_rmult well_ord_Memrel lt_Ord2)
apply (simp add: ordertype_pred_unfold well_ord_rmult well_ord_Memrel lt_Ord2)
apply (rule bexI [of _ i'])
apply (rule bexI [of _ j'])
apply (simp add: ordertype_pred_Pair_lemma ltI omult_def [symmetric])
apply (simp_all add: lt_def)
done

lemma omult_unfold:
"⟦Ord(i);  Ord(j)⟧ ⟹ j**i = (⋃j'∈j. ⋃i'∈i. {j**i' ++ j'})"
apply (rule subsetI [THEN equalityI])
apply (rule lt_omult [THEN exE])
apply (erule_tac [3] ltI)
apply (simp_all add: Ord_omult)
apply (blast elim!: ltE)
apply (blast intro: omult_oadd_lt [THEN ltD] ltI)
done

subsubsection‹Basic laws for ordinal multiplication›

text‹Ordinal multiplication by zero›

lemma omult_0 [simp]: "i**0 = 0"
unfolding omult_def
apply (simp (no_asm_simp))
done

lemma omult_0_left [simp]: "0**i = 0"
unfolding omult_def
apply (simp (no_asm_simp))
done

text‹Ordinal multiplication by 1›

lemma omult_1 [simp]: "Ord(i) ⟹ i**1 = i"
unfolding omult_def
apply (rule_tac s1="Memrel(i)"
in ord_isoI [THEN ordertype_eq, THEN trans])
apply (rule_tac c = snd and d = "λz.⟨0,z⟩"  in lam_bijective)
apply (auto elim!: snd_type well_ord_Memrel ordertype_Memrel)
done

lemma omult_1_left [simp]: "Ord(i) ⟹ 1**i = i"
unfolding omult_def
apply (rule_tac s1="Memrel(i)"
in ord_isoI [THEN ordertype_eq, THEN trans])
apply (rule_tac c = fst and d = "λz.⟨z,0⟩" in lam_bijective)
apply (auto elim!: fst_type well_ord_Memrel ordertype_Memrel)
done

text‹Distributive law for ordinal multiplication and addition›

"⟦Ord(i);  Ord(j);  Ord(k)⟧ ⟹ i**(j++k) = (i**j)++(i**k)"
apply (rule ordertype_eq [THEN trans])
apply (rule prod_ord_iso_cong [OF ordertype_ord_iso [THEN ord_iso_sym]
ord_iso_refl])
Ord_ordertype)
apply (rule sum_prod_distrib_ord_iso [THEN ordertype_eq, THEN trans])
apply (rule_tac [2] ordertype_eq)
apply (rule_tac [2] sum_ord_iso_cong [OF ordertype_ord_iso ordertype_ord_iso])
Ord_ordertype)
done

lemma omult_succ: "⟦Ord(i);  Ord(j)⟧ ⟹ i**succ(j) = (i**j)++i"

text‹Associative law›

lemma omult_assoc:
"⟦Ord(i);  Ord(j);  Ord(k)⟧ ⟹ (i**j)**k = i**(j**k)"
unfolding omult_def
apply (rule ordertype_eq [THEN trans])
apply (rule prod_ord_iso_cong [OF ord_iso_refl
ordertype_ord_iso [THEN ord_iso_sym]])
apply (blast intro: well_ord_rmult well_ord_Memrel)+
apply (rule prod_assoc_ord_iso
[THEN ord_iso_sym, THEN ordertype_eq, THEN trans])
apply (rule_tac [2] ordertype_eq)
apply (rule_tac [2] prod_ord_iso_cong [OF ordertype_ord_iso ord_iso_refl])
apply (blast intro: well_ord_rmult well_ord_Memrel Ord_ordertype)+
done

text‹Ordinal multiplication with limit ordinals›

lemma omult_UN:
"⟦Ord(i);  ⋀x. x ∈ A ⟹ Ord(j(x))⟧
⟹ i ** (⋃x∈A. j(x)) = (⋃x∈A. i**j(x))"
by (simp (no_asm_simp) add: Ord_UN omult_unfold, blast)

lemma omult_Limit: "⟦Ord(i);  Limit(j)⟧ ⟹ i**j = (⋃k∈j. i**k)"
by (simp add: Limit_is_Ord [THEN Ord_in_Ord] omult_UN [symmetric]
Union_eq_UN [symmetric] Limit_Union_eq)

subsubsection‹Ordering/monotonicity properties of ordinal multiplication›

(*As a special case we have "⟦0<i;  0<j⟧ ⟹ 0 < i**j" *)
lemma lt_omult1: "⟦k<i;  0<j⟧ ⟹ k < i**j"
apply (safe elim!: ltE intro!: ltI Ord_omult)
apply (force simp add: omult_unfold)
done

lemma omult_le_self: "⟦Ord(i);  0<j⟧ ⟹ i ≤ i**j"
by (blast intro: all_lt_imp_le Ord_omult lt_omult1 lt_Ord2)

lemma omult_le_mono1:
assumes kj: "k ≤ j" and i: "Ord(i)" shows "k**i ≤ j**i"
proof -
have o: "Ord(k)" "Ord(j)" by (rule lt_Ord [OF kj] le_Ord2 [OF kj])+
show ?thesis using i
proof (induct i rule: trans_induct3)
case 0 thus ?case
by simp
next
case (succ i) thus ?case
by (simp add: o kj omult_succ oadd_le_mono)
next
case (limit l)
thus ?case
by (auto simp add: o kj omult_Limit le_implies_UN_le_UN)
qed
qed

lemma omult_lt_mono2: "⟦k<j;  0<i⟧ ⟹ i**k < i**j"
apply (rule ltI)
apply (simp (no_asm_simp) add: omult_unfold lt_Ord2)
apply (safe elim!: ltE intro!: Ord_omult)
apply (force simp add: Ord_omult)
done

lemma omult_le_mono2: "⟦k ≤ j;  Ord(i)⟧ ⟹ i**k ≤ i**j"
apply (rule subset_imp_le)
apply (safe elim!: ltE dest!: Ord_succD intro!: Ord_omult)
apply (simp add: omult_unfold)
apply (blast intro: Ord_trans)
done

lemma omult_le_mono: "⟦i' ≤ i;  j' ≤ j⟧ ⟹ i'**j' ≤ i**j"
by (blast intro: le_trans omult_le_mono1 omult_le_mono2 Ord_succD elim: ltE)

lemma omult_lt_mono: "⟦i' ≤ i;  j'<j;  0<i⟧ ⟹ i'**j' < i**j"
by (blast intro: lt_trans1 omult_le_mono1 omult_lt_mono2 Ord_succD elim: ltE)

lemma omult_le_self2:
assumes i: "Ord(i)" and j: "0<j" shows "i ≤ j**i"
proof -
have oj: "Ord(j)" by (rule lt_Ord2 [OF j])
show ?thesis using i
proof (induct i rule: trans_induct3)
case 0 thus ?case
by simp
next
case (succ i)
have "j ** i ++ 0 < j ** i ++ j"
by (rule oadd_lt_mono2 [OF j])
with succ.hyps show ?case
by (simp add: oj j omult_succ ) (rule lt_trans1)
next
case (limit l)
hence "l = (⋃x∈l. x)"
by (simp add: Union_eq_UN [symmetric] Limit_Union_eq)
also have "... ≤ (⋃x∈l. j**x)"
by (rule le_implies_UN_le_UN) (rule limit.hyps)
finally have "l ≤ (⋃x∈l. j**x)" .
thus ?case using limit.hyps by (simp add: oj omult_Limit)
qed
qed

text‹Further properties of ordinal multiplication›

lemma omult_inject: "⟦i**j = i**k;  0<i;  Ord(j);  Ord(k)⟧ ⟹ j=k"
apply (rule Ord_linear_lt)
prefer 4 apply assumption
apply auto
apply (force dest: omult_lt_mono2 simp add: lt_not_refl)+
done

subsection‹The Relation \<^term>‹Lt››

lemma wf_Lt: "wf(Lt)"
apply (rule wf_subset)
apply (rule wf_Memrel)
apply (auto simp add: Lt_def Memrel_def lt_def)
done

lemma irrefl_Lt: "irrefl(A,Lt)"
by (auto simp add: Lt_def irrefl_def)

lemma trans_Lt: "trans[A](Lt)"
apply (simp add: Lt_def trans_on_def)
apply (blast intro: lt_trans)
done

lemma part_ord_Lt: "part_ord(A,Lt)"
by (simp add: part_ord_def irrefl_Lt trans_Lt)

lemma linear_Lt: "linear(nat,Lt)"
apply (auto dest!: not_lt_imp_le simp add: Lt_def linear_def le_iff)
apply (drule lt_asym, auto)
done

lemma tot_ord_Lt: "tot_ord(nat,Lt)"
by (simp add: tot_ord_def linear_Lt part_ord_Lt)

lemma well_ord_Lt: "well_ord(nat,Lt)"
by (simp add: well_ord_def wf_Lt wf_imp_wf_on tot_ord_Lt)

end
```