# Theory Ordinal

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theory Ordinal
imports WF Bool equalities
begin

    (*  Title:      ZF/Ordinal.thy
        ID:         $Id: Ordinal.thy,v 1.24 2005/06/17 14:15:09 haftmann Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1994  University of Cambridge

    *)

    header{*Transitive Sets and Ordinals*}

    theory Ordinal imports WF Bool equalities begin

    constdefs

      Memrel        :: "i=>i"
        "Memrel(A)   == {z: A*A . EX x y. z=<x,y> & x:y }"

      Transset  :: "i=>o"
        "Transset(i) == ALL x:i. x<=i"

      Ord  :: "i=>o"
        "Ord(i)      == Transset(i) & (ALL x:i. Transset(x))"

      lt        :: "[i,i] => o"  (infixl "<" 50)   (*less-than on ordinals*)
        "i<j         == i:j & Ord(j)"

      Limit         :: "i=>o"
        "Limit(i)    == Ord(i) & 0<i & (ALL y. y<i --> succ(y)<i)"

    syntax
      "le"          :: "[i,i] => o"  (infixl 50)   (*less-than or equals*)

    translations
      "x le y"      == "x < succ(y)"

    syntax (xsymbols)
      "op le"       :: "[i,i] => o"  (infixl "≤" 50)  (*less-than or equals*)
    syntax (HTML output)
      "op le"       :: "[i,i] => o"  (infixl "≤" 50)  (*less-than or equals*)

    subsection{*Rules for Transset*}

    subsubsection{*Three Neat Characterisations of Transset*}

    lemma Transset_iff_Pow: "Transset(A) <-> A<=Pow(A)"
    by (unfold Transset_def, blast)

    lemma Transset_iff_Union_succ: "Transset(A) <-> Union(succ(A)) = A"
    apply (unfold Transset_def)
    apply (blast elim!: equalityE)
    done

    lemma Transset_iff_Union_subset: "Transset(A) <-> Union(A) <= A"
    by (unfold Transset_def, blast)

    subsubsection{*Consequences of Downwards Closure*}

    lemma Transset_doubleton_D:
        "[| Transset(C); {a,b}: C |] ==> a:C & b: C"
    by (unfold Transset_def, blast)

    lemma Transset_Pair_D:
        "[| Transset(C); <a,b>: C |] ==> a:C & b: C"
    apply (simp add: Pair_def)
    apply (blast dest: Transset_doubleton_D)
    done

    lemma Transset_includes_domain:
        "[| Transset(C); A*B <= C; b: B |] ==> A <= C"
    by (blast dest: Transset_Pair_D)

    lemma Transset_includes_range:
        "[| Transset(C); A*B <= C; a: A |] ==> B <= C"
    by (blast dest: Transset_Pair_D)

    subsubsection{*Closure Properties*}

    lemma Transset_0: "Transset(0)"
    by (unfold Transset_def, blast)

    lemma Transset_Un:
        "[| Transset(i);  Transset(j) |] ==> Transset(i Un j)"
    by (unfold Transset_def, blast)

    lemma Transset_Int:
        "[| Transset(i);  Transset(j) |] ==> Transset(i Int j)"
    by (unfold Transset_def, blast)

    lemma Transset_succ: "Transset(i) ==> Transset(succ(i))"
    by (unfold Transset_def, blast)

    lemma Transset_Pow: "Transset(i) ==> Transset(Pow(i))"
    by (unfold Transset_def, blast)

    lemma Transset_Union: "Transset(A) ==> Transset(Union(A))"
    by (unfold Transset_def, blast)

    lemma Transset_Union_family:
        "[| !!i. i:A ==> Transset(i) |] ==> Transset(Union(A))"
    by (unfold Transset_def, blast)

    lemma Transset_Inter_family:
        "[| !!i. i:A ==> Transset(i) |] ==> Transset(Inter(A))"
    by (unfold Inter_def Transset_def, blast)

    lemma Transset_UN:
         "(!!x. x ∈ A ==> Transset(B(x))) ==> Transset (\<Union>x∈A. B(x))"
    by (rule Transset_Union_family, auto)

    lemma Transset_INT:
         "(!!x. x ∈ A ==> Transset(B(x))) ==> Transset (\<Inter>x∈A. B(x))"
    by (rule Transset_Inter_family, auto)

    subsection{*Lemmas for Ordinals*}

    lemma OrdI:
        "[| Transset(i);  !!x. x:i ==> Transset(x) |]  ==>  Ord(i)"
    by (simp add: Ord_def)

    lemma Ord_is_Transset: "Ord(i) ==> Transset(i)"
    by (simp add: Ord_def)

    lemma Ord_contains_Transset:
        "[| Ord(i);  j:i |] ==> Transset(j) "
    by (unfold Ord_def, blast)

    lemma Ord_in_Ord: "[| Ord(i);  j:i |] ==> Ord(j)"
    by (unfold Ord_def Transset_def, blast)

    (*suitable for rewriting PROVIDED i has been fixed*)
    lemma Ord_in_Ord': "[| j:i; Ord(i) |] ==> Ord(j)"
    by (blast intro: Ord_in_Ord)

    (* Ord(succ(j)) ==> Ord(j) *)
    lemmas Ord_succD = Ord_in_Ord [OF _ succI1]

    lemma Ord_subset_Ord: "[| Ord(i);  Transset(j);  j<=i |] ==> Ord(j)"
    by (simp add: Ord_def Transset_def, blast)

    lemma OrdmemD: "[| j:i;  Ord(i) |] ==> j<=i"
    by (unfold Ord_def Transset_def, blast)

    lemma Ord_trans: "[| i:j;  j:k;  Ord(k) |] ==> i:k"
    by (blast dest: OrdmemD)

    lemma Ord_succ_subsetI: "[| i:j;  Ord(j) |] ==> succ(i) <= j"
    by (blast dest: OrdmemD)

    subsection{*The Construction of Ordinals: 0, succ, Union*}

    lemma Ord_0 [iff,TC]: "Ord(0)"
    by (blast intro: OrdI Transset_0)

    lemma Ord_succ [TC]: "Ord(i) ==> Ord(succ(i))"
    by (blast intro: OrdI Transset_succ Ord_is_Transset Ord_contains_Transset)

    lemmas Ord_1 = Ord_0 [THEN Ord_succ]

    lemma Ord_succ_iff [iff]: "Ord(succ(i)) <-> Ord(i)"
    by (blast intro: Ord_succ dest!: Ord_succD)

    lemma Ord_Un [intro,simp,TC]: "[| Ord(i); Ord(j) |] ==> Ord(i Un j)"
    apply (unfold Ord_def)
    apply (blast intro!: Transset_Un)
    done

    lemma Ord_Int [TC]: "[| Ord(i); Ord(j) |] ==> Ord(i Int j)"
    apply (unfold Ord_def)
    apply (blast intro!: Transset_Int)
    done

    (*There is no set of all ordinals, for then it would contain itself*)
    lemma ON_class: "~ (ALL i. i:X <-> Ord(i))"
    apply (rule notI)
    apply (frule_tac x = X in spec)
    apply (safe elim!: mem_irrefl)
    apply (erule swap, rule OrdI [OF _ Ord_is_Transset])
    apply (simp add: Transset_def)
    apply (blast intro: Ord_in_Ord)+
    done

    subsection{*< is 'less Than' for Ordinals*}

    lemma ltI: "[| i:j;  Ord(j) |] ==> i<j"
    by (unfold lt_def, blast)

    lemma ltE:
        "[| i<j;  [| i:j;  Ord(i);  Ord(j) |] ==> P |] ==> P"
    apply (unfold lt_def)
    apply (blast intro: Ord_in_Ord)
    done

    lemma ltD: "i<j ==> i:j"
    by (erule ltE, assumption)

    lemma not_lt0 [simp]: "~ i<0"
    by (unfold lt_def, blast)

    lemma lt_Ord: "j<i ==> Ord(j)"
    by (erule ltE, assumption)

    lemma lt_Ord2: "j<i ==> Ord(i)"
    by (erule ltE, assumption)

    (* "ja le j ==> Ord(j)" *)
    lemmas le_Ord2 = lt_Ord2 [THEN Ord_succD]

    (* i<0 ==> R *)
    lemmas lt0E = not_lt0 [THEN notE, elim!]

    lemma lt_trans: "[| i<j;  j<k |] ==> i<k"
    by (blast intro!: ltI elim!: ltE intro: Ord_trans)

    lemma lt_not_sym: "i<j ==> ~ (j<i)"
    apply (unfold lt_def)
    apply (blast elim: mem_asym)
    done

    (* [| i<j;  ~P ==> j<i |] ==> P *)
    lemmas lt_asym = lt_not_sym [THEN swap]

    lemma lt_irrefl [elim!]: "i<i ==> P"
    by (blast intro: lt_asym)

    lemma lt_not_refl: "~ i<i"
    apply (rule notI)
    apply (erule lt_irrefl)
    done

    (** le is less than or equals;  recall  i le j  abbrevs  i<succ(j) !! **)

    lemma le_iff: "i le j <-> i<j | (i=j & Ord(j))"
    by (unfold lt_def, blast)

    (*Equivalently, i<j ==> i < succ(j)*)
    lemma leI: "i<j ==> i le j"
    by (simp (no_asm_simp) add: le_iff)

    lemma le_eqI: "[| i=j;  Ord(j) |] ==> i le j"
    by (simp (no_asm_simp) add: le_iff)

    lemmas le_refl = refl [THEN le_eqI]

    lemma le_refl_iff [iff]: "i le i <-> Ord(i)"
    by (simp (no_asm_simp) add: lt_not_refl le_iff)

    lemma leCI: "(~ (i=j & Ord(j)) ==> i<j) ==> i le j"
    by (simp add: le_iff, blast)

    lemma leE:
        "[| i le j;  i<j ==> P;  [| i=j;  Ord(j) |] ==> P |] ==> P"
    by (simp add: le_iff, blast)

    lemma le_anti_sym: "[| i le j;  j le i |] ==> i=j"
    apply (simp add: le_iff)
    apply (blast elim: lt_asym)
    done

    lemma le0_iff [simp]: "i le 0 <-> i=0"
    by (blast elim!: leE)

    lemmas le0D = le0_iff [THEN iffD1, dest!]

    subsection{*Natural Deduction Rules for Memrel*}

    (*The lemmas MemrelI/E give better speed than [iff] here*)
    lemma Memrel_iff [simp]: "<a,b> : Memrel(A) <-> a:b & a:A & b:A"
    by (unfold Memrel_def, blast)

    lemma MemrelI [intro!]: "[| a: b;  a: A;  b: A |] ==> <a,b> : Memrel(A)"
    by auto

    lemma MemrelE [elim!]:
        "[| <a,b> : Memrel(A);
            [| a: A;  b: A;  a:b |]  ==> P |]
         ==> P"
    by auto

    lemma Memrel_type: "Memrel(A) <= A*A"
    by (unfold Memrel_def, blast)

    lemma Memrel_mono: "A<=B ==> Memrel(A) <= Memrel(B)"
    by (unfold Memrel_def, blast)

    lemma Memrel_0 [simp]: "Memrel(0) = 0"
    by (unfold Memrel_def, blast)

    lemma Memrel_1 [simp]: "Memrel(1) = 0"
    by (unfold Memrel_def, blast)

    lemma relation_Memrel: "relation(Memrel(A))"
    by (simp add: relation_def Memrel_def)

    (*The membership relation (as a set) is well-founded.
      Proof idea: show A<=B by applying the foundation axiom to A-B *)
    lemma wf_Memrel: "wf(Memrel(A))"
    apply (unfold wf_def)
    apply (rule foundation [THEN disjE, THEN allI], erule disjI1, blast)
    done

    text{*The premise @{term "Ord(i)"} does not suffice.*}
    lemma trans_Memrel:
        "Ord(i) ==> trans(Memrel(i))"
    by (unfold Ord_def Transset_def trans_def, blast)

    text{*However, the following premise is strong enough.*}
    lemma Transset_trans_Memrel:
        "∀j∈i. Transset(j) ==> trans(Memrel(i))"
    by (unfold Transset_def trans_def, blast)

    (*If Transset(A) then Memrel(A) internalizes the membership relation below A*)
    lemma Transset_Memrel_iff:
        "Transset(A) ==> <a,b> : Memrel(A) <-> a:b & b:A"
    by (unfold Transset_def, blast)

    subsection{*Transfinite Induction*}

    (*Epsilon induction over a transitive set*)
    lemma Transset_induct:
        "[| i: k;  Transset(k);
            !!x.[| x: k;  ALL y:x. P(y) |] ==> P(x) |]
         ==>  P(i)"
    apply (simp add: Transset_def)
    apply (erule wf_Memrel [THEN wf_induct2], blast+)
    done

    (*Induction over an ordinal*)
    lemmas Ord_induct [consumes 2] = Transset_induct [OF _ Ord_is_Transset]
    lemmas Ord_induct_rule = Ord_induct [rule_format, consumes 2]

    (*Induction over the class of ordinals -- a useful corollary of Ord_induct*)

    lemma trans_induct [consumes 1]:
        "[| Ord(i);
            !!x.[| Ord(x);  ALL y:x. P(y) |] ==> P(x) |]
         ==>  P(i)"
    apply (rule Ord_succ [THEN succI1 [THEN Ord_induct]], assumption)
    apply (blast intro: Ord_succ [THEN Ord_in_Ord])
    done

    lemmas trans_induct_rule = trans_induct [rule_format, consumes 1]

    (*** Fundamental properties of the epsilon ordering (< on ordinals) ***)

    subsubsection{*Proving That < is a Linear Ordering on the Ordinals*}

    lemma Ord_linear [rule_format]:
         "Ord(i) ==> (ALL j. Ord(j) --> i:j | i=j | j:i)"
    apply (erule trans_induct)
    apply (rule impI [THEN allI])
    apply (erule_tac i=j in trans_induct)
    apply (blast dest: Ord_trans)
    done

    (*The trichotomy law for ordinals!*)
    lemma Ord_linear_lt:
        "[| Ord(i);  Ord(j);  i<j ==> P;  i=j ==> P;  j<i ==> P |] ==> P"
    apply (simp add: lt_def)
    apply (rule_tac i1=i and j1=j in Ord_linear [THEN disjE], blast+)
    done

    lemma Ord_linear2:
        "[| Ord(i);  Ord(j);  i<j ==> P;  j le i ==> P |]  ==> P"
    apply (rule_tac i = i and j = j in Ord_linear_lt)
    apply (blast intro: leI le_eqI sym ) +
    done

    lemma Ord_linear_le:
        "[| Ord(i);  Ord(j);  i le j ==> P;  j le i ==> P |]  ==> P"
    apply (rule_tac i = i and j = j in Ord_linear_lt)
    apply (blast intro: leI le_eqI ) +
    done

    lemma le_imp_not_lt: "j le i ==> ~ i<j"
    by (blast elim!: leE elim: lt_asym)

    lemma not_lt_imp_le: "[| ~ i<j;  Ord(i);  Ord(j) |] ==> j le i"
    by (rule_tac i = i and j = j in Ord_linear2, auto)

    subsubsection{*Some Rewrite Rules for <, le*}

    lemma Ord_mem_iff_lt: "Ord(j) ==> i:j <-> i<j"
    by (unfold lt_def, blast)

    lemma not_lt_iff_le: "[| Ord(i);  Ord(j) |] ==> ~ i<j <-> j le i"
    by (blast dest: le_imp_not_lt not_lt_imp_le)

    lemma not_le_iff_lt: "[| Ord(i);  Ord(j) |] ==> ~ i le j <-> j<i"
    by (simp (no_asm_simp) add: not_lt_iff_le [THEN iff_sym])

    (*This is identical to 0<succ(i) *)
    lemma Ord_0_le: "Ord(i) ==> 0 le i"
    by (erule not_lt_iff_le [THEN iffD1], auto)

    lemma Ord_0_lt: "[| Ord(i);  i~=0 |] ==> 0<i"
    apply (erule not_le_iff_lt [THEN iffD1])
    apply (rule Ord_0, blast)
    done

    lemma Ord_0_lt_iff: "Ord(i) ==> i~=0 <-> 0<i"
    by (blast intro: Ord_0_lt)

    subsection{*Results about Less-Than or Equals*}

    (** For ordinals, j<=i (subset) implies j le i (less-than or equals) **)

    lemma zero_le_succ_iff [iff]: "0 le succ(x) <-> Ord(x)"
    by (blast intro: Ord_0_le elim: ltE)

    lemma subset_imp_le: "[| j<=i;  Ord(i);  Ord(j) |] ==> j le i"
    apply (rule not_lt_iff_le [THEN iffD1], assumption+)
    apply (blast elim: ltE mem_irrefl)
    done

    lemma le_imp_subset: "i le j ==> i<=j"
    by (blast dest: OrdmemD elim: ltE leE)

    lemma le_subset_iff: "j le i <-> j<=i & Ord(i) & Ord(j)"
    by (blast dest: subset_imp_le le_imp_subset elim: ltE)

    lemma le_succ_iff: "i le succ(j) <-> i le j | i=succ(j) & Ord(i)"
    apply (simp (no_asm) add: le_iff)
    apply blast
    done

    (*Just a variant of subset_imp_le*)
    lemma all_lt_imp_le: "[| Ord(i);  Ord(j);  !!x. x<j ==> x<i |] ==> j le i"
    by (blast intro: not_lt_imp_le dest: lt_irrefl)

    subsubsection{*Transitivity Laws*}

    lemma lt_trans1: "[| i le j;  j<k |] ==> i<k"
    by (blast elim!: leE intro: lt_trans)

    lemma lt_trans2: "[| i<j;  j le k |] ==> i<k"
    by (blast elim!: leE intro: lt_trans)

    lemma le_trans: "[| i le j;  j le k |] ==> i le k"
    by (blast intro: lt_trans1)

    lemma succ_leI: "i<j ==> succ(i) le j"
    apply (rule not_lt_iff_le [THEN iffD1])
    apply (blast elim: ltE leE lt_asym)+
    done

    (*Identical to  succ(i) < succ(j) ==> i<j  *)
    lemma succ_leE: "succ(i) le j ==> i<j"
    apply (rule not_le_iff_lt [THEN iffD1])
    apply (blast elim: ltE leE lt_asym)+
    done

    lemma succ_le_iff [iff]: "succ(i) le j <-> i<j"
    by (blast intro: succ_leI succ_leE)

    lemma succ_le_imp_le: "succ(i) le succ(j) ==> i le j"
    by (blast dest!: succ_leE)

    lemma lt_subset_trans: "[| i <= j;  j<k;  Ord(i) |] ==> i<k"
    apply (rule subset_imp_le [THEN lt_trans1])
    apply (blast intro: elim: ltE) +
    done

    lemma lt_imp_0_lt: "j<i ==> 0<i"
    by (blast intro: lt_trans1 Ord_0_le [OF lt_Ord])

    lemma succ_lt_iff: "succ(i) < j <-> i<j & succ(i) ≠ j"
    apply auto
    apply (blast intro: lt_trans le_refl dest: lt_Ord)
    apply (frule lt_Ord)
    apply (rule not_le_iff_lt [THEN iffD1])
      apply (blast intro: lt_Ord2)
     apply blast
    apply (simp add: lt_Ord lt_Ord2 le_iff)
    apply (blast dest: lt_asym)
    done

    lemma Ord_succ_mem_iff: "Ord(j) ==> succ(i) ∈ succ(j) <-> i∈j"
    apply (insert succ_le_iff [of i j])
    apply (simp add: lt_def)
    done

    subsubsection{*Union and Intersection*}

    lemma Un_upper1_le: "[| Ord(i); Ord(j) |] ==> i le i Un j"
    by (rule Un_upper1 [THEN subset_imp_le], auto)

    lemma Un_upper2_le: "[| Ord(i); Ord(j) |] ==> j le i Un j"
    by (rule Un_upper2 [THEN subset_imp_le], auto)

    (*Replacing k by succ(k') yields the similar rule for le!*)
    lemma Un_least_lt: "[| i<k;  j<k |] ==> i Un j < k"
    apply (rule_tac i = i and j = j in Ord_linear_le)
    apply (auto simp add: Un_commute le_subset_iff subset_Un_iff lt_Ord)
    done

    lemma Un_least_lt_iff: "[| Ord(i); Ord(j) |] ==> i Un j < k  <->  i<k & j<k"
    apply (safe intro!: Un_least_lt)
    apply (rule_tac [2] Un_upper2_le [THEN lt_trans1])
    apply (rule Un_upper1_le [THEN lt_trans1], auto)
    done

    lemma Un_least_mem_iff:
        "[| Ord(i); Ord(j); Ord(k) |] ==> i Un j : k  <->  i:k & j:k"
    apply (insert Un_least_lt_iff [of i j k])
    apply (simp add: lt_def)
    done

    (*Replacing k by succ(k') yields the similar rule for le!*)
    lemma Int_greatest_lt: "[| i<k;  j<k |] ==> i Int j < k"
    apply (rule_tac i = i and j = j in Ord_linear_le)
    apply (auto simp add: Int_commute le_subset_iff subset_Int_iff lt_Ord)
    done

    lemma Ord_Un_if:
         "[| Ord(i); Ord(j) |] ==> i ∪ j = (if j<i then i else j)"
    by (simp add: not_lt_iff_le le_imp_subset leI
                  subset_Un_iff [symmetric]  subset_Un_iff2 [symmetric])

    lemma succ_Un_distrib:
         "[| Ord(i); Ord(j) |] ==> succ(i ∪ j) = succ(i) ∪ succ(j)"
    by (simp add: Ord_Un_if lt_Ord le_Ord2)

    lemma lt_Un_iff:
         "[| Ord(i); Ord(j) |] ==> k < i ∪ j <-> k < i | k < j";
    apply (simp add: Ord_Un_if not_lt_iff_le)
    apply (blast intro: leI lt_trans2)+
    done

    lemma le_Un_iff:
         "[| Ord(i); Ord(j) |] ==> k ≤ i ∪ j <-> k ≤ i | k ≤ j";
    by (simp add: succ_Un_distrib lt_Un_iff [symmetric])

    lemma Un_upper1_lt: "[|k < i; Ord(j)|] ==> k < i Un j"
    by (simp add: lt_Un_iff lt_Ord2)

    lemma Un_upper2_lt: "[|k < j; Ord(i)|] ==> k < i Un j"
    by (simp add: lt_Un_iff lt_Ord2)

    (*See also Transset_iff_Union_succ*)
    lemma Ord_Union_succ_eq: "Ord(i) ==> \<Union>(succ(i)) = i"
    by (blast intro: Ord_trans)

    subsection{*Results about Limits*}

    lemma Ord_Union [intro,simp,TC]: "[| !!i. i:A ==> Ord(i) |] ==> Ord(Union(A))"
    apply (rule Ord_is_Transset [THEN Transset_Union_family, THEN OrdI])
    apply (blast intro: Ord_contains_Transset)+
    done

    lemma Ord_UN [intro,simp,TC]:
         "[| !!x. x:A ==> Ord(B(x)) |] ==> Ord(\<Union>x∈A. B(x))"
    by (rule Ord_Union, blast)

    lemma Ord_Inter [intro,simp,TC]:
        "[| !!i. i:A ==> Ord(i) |] ==> Ord(Inter(A))"
    apply (rule Transset_Inter_family [THEN OrdI])
    apply (blast intro: Ord_is_Transset)
    apply (simp add: Inter_def)
    apply (blast intro: Ord_contains_Transset)
    done

    lemma Ord_INT [intro,simp,TC]:
        "[| !!x. x:A ==> Ord(B(x)) |] ==> Ord(\<Inter>x∈A. B(x))"
    by (rule Ord_Inter, blast)

    (* No < version; consider (\<Union>i∈nat.i)=nat *)
    lemma UN_least_le:
        "[| Ord(i);  !!x. x:A ==> b(x) le i |] ==> (\<Union>x∈A. b(x)) le i"
    apply (rule le_imp_subset [THEN UN_least, THEN subset_imp_le])
    apply (blast intro: Ord_UN elim: ltE)+
    done

    lemma UN_succ_least_lt:
        "[| j<i;  !!x. x:A ==> b(x)<j |] ==> (\<Union>x∈A. succ(b(x))) < i"
    apply (rule ltE, assumption)
    apply (rule UN_least_le [THEN lt_trans2])
    apply (blast intro: succ_leI)+
    done

    lemma UN_upper_lt:
         "[| a∈A;  i < b(a);  Ord(\<Union>x∈A. b(x)) |] ==> i < (\<Union>x∈A. b(x))"
    by (unfold lt_def, blast)

    lemma UN_upper_le:
         "[| a: A;  i le b(a);  Ord(\<Union>x∈A. b(x)) |] ==> i le (\<Union>x∈A. b(x))"
    apply (frule ltD)
    apply (rule le_imp_subset [THEN subset_trans, THEN subset_imp_le])
    apply (blast intro: lt_Ord UN_upper)+
    done

    lemma lt_Union_iff: "∀i∈A. Ord(i) ==> (j < \<Union>(A)) <-> (∃i∈A. j<i)"
    by (auto simp: lt_def Ord_Union)

    lemma Union_upper_le:
         "[| j: J;  i≤j;  Ord(\<Union>(J)) |] ==> i ≤ \<Union>J"
    apply (subst Union_eq_UN)
    apply (rule UN_upper_le, auto)
    done

    lemma le_implies_UN_le_UN:
        "[| !!x. x:A ==> c(x) le d(x) |] ==> (\<Union>x∈A. c(x)) le (\<Union>x∈A. d(x))"
    apply (rule UN_least_le)
    apply (rule_tac [2] UN_upper_le)
    apply (blast intro: Ord_UN le_Ord2)+
    done

    lemma Ord_equality: "Ord(i) ==> (\<Union>y∈i. succ(y)) = i"
    by (blast intro: Ord_trans)

    (*Holds for all transitive sets, not just ordinals*)
    lemma Ord_Union_subset: "Ord(i) ==> Union(i) <= i"
    by (blast intro: Ord_trans)

    subsection{*Limit Ordinals -- General Properties*}

    lemma Limit_Union_eq: "Limit(i) ==> Union(i) = i"
    apply (unfold Limit_def)
    apply (fast intro!: ltI elim!: ltE elim: Ord_trans)
    done

    lemma Limit_is_Ord: "Limit(i) ==> Ord(i)"
    apply (unfold Limit_def)
    apply (erule conjunct1)
    done

    lemma Limit_has_0: "Limit(i) ==> 0 < i"
    apply (unfold Limit_def)
    apply (erule conjunct2 [THEN conjunct1])
    done

    lemma Limit_nonzero: "Limit(i) ==> i ~= 0"
    by (drule Limit_has_0, blast)

    lemma Limit_has_succ: "[| Limit(i);  j<i |] ==> succ(j) < i"
    by (unfold Limit_def, blast)

    lemma Limit_succ_lt_iff [simp]: "Limit(i) ==> succ(j) < i <-> (j<i)"
    apply (safe intro!: Limit_has_succ)
    apply (frule lt_Ord)
    apply (blast intro: lt_trans)
    done

    lemma zero_not_Limit [iff]: "~ Limit(0)"
    by (simp add: Limit_def)

    lemma Limit_has_1: "Limit(i) ==> 1 < i"
    by (blast intro: Limit_has_0 Limit_has_succ)

    lemma increasing_LimitI: "[| 0<l; ∀x∈l. ∃y∈l. x<y |] ==> Limit(l)"
    apply (unfold Limit_def, simp add: lt_Ord2, clarify)
    apply (drule_tac i=y in ltD)
    apply (blast intro: lt_trans1 [OF _ ltI] lt_Ord2)
    done

    lemma non_succ_LimitI:
        "[| 0<i;  ALL y. succ(y) ~= i |] ==> Limit(i)"
    apply (unfold Limit_def)
    apply (safe del: subsetI)
    apply (rule_tac [2] not_le_iff_lt [THEN iffD1])
    apply (simp_all add: lt_Ord lt_Ord2)
    apply (blast elim: leE lt_asym)
    done

    lemma succ_LimitE [elim!]: "Limit(succ(i)) ==> P"
    apply (rule lt_irrefl)
    apply (rule Limit_has_succ, assumption)
    apply (erule Limit_is_Ord [THEN Ord_succD, THEN le_refl])
    done

    lemma not_succ_Limit [simp]: "~ Limit(succ(i))"
    by blast

    lemma Limit_le_succD: "[| Limit(i);  i le succ(j) |] ==> i le j"
    by (blast elim!: leE)

    subsubsection{*Traditional 3-Way Case Analysis on Ordinals*}

    lemma Ord_cases_disj: "Ord(i) ==> i=0 | (EX j. Ord(j) & i=succ(j)) | Limit(i)"
    by (blast intro!: non_succ_LimitI Ord_0_lt)

    lemma Ord_cases:
        "[| Ord(i);
            i=0                          ==> P;
            !!j. [| Ord(j); i=succ(j) |] ==> P;
            Limit(i)                     ==> P
         |] ==> P"
    by (drule Ord_cases_disj, blast)

    lemma trans_induct3 [case_names 0 succ limit, consumes 1]:
         "[| Ord(i);
             P(0);
             !!x. [| Ord(x);  P(x) |] ==> P(succ(x));
             !!x. [| Limit(x);  ALL y:x. P(y) |] ==> P(x)
          |] ==> P(i)"
    apply (erule trans_induct)
    apply (erule Ord_cases, blast+)
    done

    lemmas trans_induct3_rule = trans_induct3 [rule_format, case_names 0 succ limit, consumes 1]

    text{*A set of ordinals is either empty, contains its own union, or its
    union is a limit ordinal.*}
    lemma Ord_set_cases:
       "∀i∈I. Ord(i) ==> I=0 ∨ \<Union>(I) ∈ I ∨ (\<Union>(I) ∉ I ∧ Limit(\<Union>(I)))"
    apply (clarify elim!: not_emptyE)
    apply (cases "\<Union>(I)" rule: Ord_cases)
       apply (blast intro: Ord_Union)
      apply (blast intro: subst_elem)
     apply auto
    apply (clarify elim!: equalityE succ_subsetE)
    apply (simp add: Union_subset_iff)
    apply (subgoal_tac "B = succ(j)", blast)
    apply (rule le_anti_sym)
     apply (simp add: le_subset_iff)
    apply (simp add: ltI)
    done

    text{*If the union of a set of ordinals is a successor, then it is
    an element of that set.*}
    lemma Ord_Union_eq_succD: "[|∀x∈X. Ord(x);  \<Union>X = succ(j)|] ==> succ(j) ∈ X"
    by (drule Ord_set_cases, auto)

    lemma Limit_Union [rule_format]: "[| I ≠ 0;  ∀i∈I. Limit(i) |] ==> Limit(\<Union>I)"
    apply (simp add: Limit_def lt_def)
    apply (blast intro!: equalityI)
    done

    ML
    {*
    val Memrel_def = thm "Memrel_def";
    val Transset_def = thm "Transset_def";
    val Ord_def = thm "Ord_def";
    val lt_def = thm "lt_def";
    val Limit_def = thm "Limit_def";

    val Transset_iff_Pow = thm "Transset_iff_Pow";
    val Transset_iff_Union_succ = thm "Transset_iff_Union_succ";
    val Transset_iff_Union_subset = thm "Transset_iff_Union_subset";
    val Transset_doubleton_D = thm "Transset_doubleton_D";
    val Transset_Pair_D = thm "Transset_Pair_D";
    val Transset_includes_domain = thm "Transset_includes_domain";
    val Transset_includes_range = thm "Transset_includes_range";
    val Transset_0 = thm "Transset_0";
    val Transset_Un = thm "Transset_Un";
    val Transset_Int = thm "Transset_Int";
    val Transset_succ = thm "Transset_succ";
    val Transset_Pow = thm "Transset_Pow";
    val Transset_Union = thm "Transset_Union";
    val Transset_Union_family = thm "Transset_Union_family";
    val Transset_Inter_family = thm "Transset_Inter_family";
    val OrdI = thm "OrdI";
    val Ord_is_Transset = thm "Ord_is_Transset";
    val Ord_contains_Transset = thm "Ord_contains_Transset";
    val Ord_in_Ord = thm "Ord_in_Ord";
    val Ord_succD = thm "Ord_succD";
    val Ord_subset_Ord = thm "Ord_subset_Ord";
    val OrdmemD = thm "OrdmemD";
    val Ord_trans = thm "Ord_trans";
    val Ord_succ_subsetI = thm "Ord_succ_subsetI";
    val Ord_0 = thm "Ord_0";
    val Ord_succ = thm "Ord_succ";
    val Ord_1 = thm "Ord_1";
    val Ord_succ_iff = thm "Ord_succ_iff";
    val Ord_Un = thm "Ord_Un";
    val Ord_Int = thm "Ord_Int";
    val Ord_Inter = thm "Ord_Inter";
    val Ord_INT = thm "Ord_INT";
    val ON_class = thm "ON_class";
    val ltI = thm "ltI";
    val ltE = thm "ltE";
    val ltD = thm "ltD";
    val not_lt0 = thm "not_lt0";
    val lt_Ord = thm "lt_Ord";
    val lt_Ord2 = thm "lt_Ord2";
    val le_Ord2 = thm "le_Ord2";
    val lt0E = thm "lt0E";
    val lt_trans = thm "lt_trans";
    val lt_not_sym = thm "lt_not_sym";
    val lt_asym = thm "lt_asym";
    val lt_irrefl = thm "lt_irrefl";
    val lt_not_refl = thm "lt_not_refl";
    val le_iff = thm "le_iff";
    val leI = thm "leI";
    val le_eqI = thm "le_eqI";
    val le_refl = thm "le_refl";
    val le_refl_iff = thm "le_refl_iff";
    val leCI = thm "leCI";
    val leE = thm "leE";
    val le_anti_sym = thm "le_anti_sym";
    val le0_iff = thm "le0_iff";
    val le0D = thm "le0D";
    val Memrel_iff = thm "Memrel_iff";
    val MemrelI = thm "MemrelI";
    val MemrelE = thm "MemrelE";
    val Memrel_type = thm "Memrel_type";
    val Memrel_mono = thm "Memrel_mono";
    val Memrel_0 = thm "Memrel_0";
    val Memrel_1 = thm "Memrel_1";
    val wf_Memrel = thm "wf_Memrel";
    val trans_Memrel = thm "trans_Memrel";
    val Transset_Memrel_iff = thm "Transset_Memrel_iff";
    val Transset_induct = thm "Transset_induct";
    val Ord_induct = thm "Ord_induct";
    val trans_induct = thm "trans_induct";
    val Ord_linear = thm "Ord_linear";
    val Ord_linear_lt = thm "Ord_linear_lt";
    val Ord_linear2 = thm "Ord_linear2";
    val Ord_linear_le = thm "Ord_linear_le";
    val le_imp_not_lt = thm "le_imp_not_lt";
    val not_lt_imp_le = thm "not_lt_imp_le";
    val Ord_mem_iff_lt = thm "Ord_mem_iff_lt";
    val not_lt_iff_le = thm "not_lt_iff_le";
    val not_le_iff_lt = thm "not_le_iff_lt";
    val Ord_0_le = thm "Ord_0_le";
    val Ord_0_lt = thm "Ord_0_lt";
    val Ord_0_lt_iff = thm "Ord_0_lt_iff";
    val zero_le_succ_iff = thm "zero_le_succ_iff";
    val subset_imp_le = thm "subset_imp_le";
    val le_imp_subset = thm "le_imp_subset";
    val le_subset_iff = thm "le_subset_iff";
    val le_succ_iff = thm "le_succ_iff";
    val all_lt_imp_le = thm "all_lt_imp_le";
    val lt_trans1 = thm "lt_trans1";
    val lt_trans2 = thm "lt_trans2";
    val le_trans = thm "le_trans";
    val succ_leI = thm "succ_leI";
    val succ_leE = thm "succ_leE";
    val succ_le_iff = thm "succ_le_iff";
    val succ_le_imp_le = thm "succ_le_imp_le";
    val lt_subset_trans = thm "lt_subset_trans";
    val Un_upper1_le = thm "Un_upper1_le";
    val Un_upper2_le = thm "Un_upper2_le";
    val Un_least_lt = thm "Un_least_lt";
    val Un_least_lt_iff = thm "Un_least_lt_iff";
    val Un_least_mem_iff = thm "Un_least_mem_iff";
    val Int_greatest_lt = thm "Int_greatest_lt";
    val Ord_Union = thm "Ord_Union";
    val Ord_UN = thm "Ord_UN";
    val UN_least_le = thm "UN_least_le";
    val UN_succ_least_lt = thm "UN_succ_least_lt";
    val UN_upper_le = thm "UN_upper_le";
    val le_implies_UN_le_UN = thm "le_implies_UN_le_UN";
    val Ord_equality = thm "Ord_equality";
    val Ord_Union_subset = thm "Ord_Union_subset";
    val Limit_Union_eq = thm "Limit_Union_eq";
    val Limit_is_Ord = thm "Limit_is_Ord";
    val Limit_has_0 = thm "Limit_has_0";
    val Limit_has_succ = thm "Limit_has_succ";
    val non_succ_LimitI = thm "non_succ_LimitI";
    val succ_LimitE = thm "succ_LimitE";
    val not_succ_Limit = thm "not_succ_Limit";
    val Limit_le_succD = thm "Limit_le_succD";
    val Ord_cases_disj = thm "Ord_cases_disj";
    val Ord_cases = thm "Ord_cases";
    val trans_induct3 = thm "trans_induct3";
    *}

    end

### Rules for Transset

#### Three Neat Characterisations of Transset

lemma Transset_iff_Pow:

      Transset(A) <-> A ⊆ Pow(A)

lemma Transset_iff_Union_succ:

      Transset(A) <-> \<Union>succ(A) = A

lemma Transset_iff_Union_subset:

      Transset(A) <-> \<Union>A ⊆ A

#### Consequences of Downwards Closure

lemma Transset_doubleton_D:

      [| Transset(C); {a, b} ∈ C |] ==> a ∈ C ∧ b ∈ C

lemma Transset_Pair_D:

      [| Transset(C); ⟨a, b⟩ ∈ C |] ==> a ∈ C ∧ b ∈ C

lemma Transset_includes_domain:

      [| Transset(C); A × B ⊆ C; b ∈ B |] ==> A ⊆ C

lemma Transset_includes_range:

      [| Transset(C); A × B ⊆ C; a ∈ A |] ==> B ⊆ C

#### Closure Properties

lemma Transset_0:

      Transset(0)

lemma Transset_Un:

      [| Transset(i); Transset(j) |] ==> Transset(i ∪ j)

lemma Transset_Int:

      [| Transset(i); Transset(j) |] ==> Transset(i ∩ j)

lemma Transset_succ:

      Transset(i) ==> Transset(succ(i))

lemma Transset_Pow:

      Transset(i) ==> Transset(Pow(i))

lemma Transset_Union:

      Transset(A) ==> Transset(\<Union>A)

lemma Transset_Union_family:

      (!!i. i ∈ A ==> Transset(i)) ==> Transset(\<Union>A)

lemma Transset_Inter_family:

      (!!i. i ∈ A ==> Transset(i)) ==> Transset(\<Inter>A)

lemma Transset_UN:

      (!!x. x ∈ A ==> Transset(B(x))) ==> Transset(\<Union>x∈A. B(x))

lemma Transset_INT:

      (!!x. x ∈ A ==> Transset(B(x))) ==> Transset(\<Inter>x∈A. B(x))

### Lemmas for Ordinals

lemma OrdI:

      [| Transset(i); !!x. x ∈ i ==> Transset(x) |] ==> Ord(i)

lemma Ord_is_Transset:

      Ord(i) ==> Transset(i)

lemma Ord_contains_Transset:

      [| Ord(i); j ∈ i |] ==> Transset(j)

lemma Ord_in_Ord:

      [| Ord(i); j ∈ i |] ==> Ord(j)

lemma Ord_in_Ord':

      [| j ∈ i; Ord(i) |] ==> Ord(j)

lemmas Ord_succD:

      Ord(succ(j)) ==> Ord(j)

lemmas Ord_succD:

      Ord(succ(j)) ==> Ord(j)

lemma Ord_subset_Ord:

      [| Ord(i); Transset(j); j ⊆ i |] ==> Ord(j)

lemma OrdmemD:

      [| j ∈ i; Ord(i) |] ==> j ⊆ i

lemma Ord_trans:

      [| i ∈ j; j ∈ k; Ord(k) |] ==> i ∈ k

lemma Ord_succ_subsetI:

      [| i ∈ j; Ord(j) |] ==> succ(i) ⊆ j

### The Construction of Ordinals: 0, succ, Union

lemma Ord_0:

      Ord(0)

lemma Ord_succ:

      Ord(i) ==> Ord(succ(i))

lemmas Ord_1:

      Ord(1)

lemmas Ord_1:

      Ord(1)

lemma Ord_succ_iff:

      Ord(succ(i)) <-> Ord(i)

lemma Ord_Un:

      [| Ord(i); Ord(j) |] ==> Ord(i ∪ j)

lemma Ord_Int:

      [| Ord(i); Ord(j) |] ==> Ord(i ∩ j)

lemma ON_class:

      ¬ (∀i. i ∈ X <-> Ord(i))

### < is 'less Than' for Ordinals

lemma ltI:

      [| i ∈ j; Ord(j) |] ==> i < j

lemma ltE:

      [| i < j; [| i ∈ j; Ord(i); Ord(j) |] ==> P |] ==> P

lemma ltD:

      i < j ==> i ∈ j

lemma not_lt0:

      ¬ i < 0

lemma lt_Ord:

      j < i ==> Ord(j)

lemma lt_Ord2:

      j < i ==> Ord(i)

lemmas le_Ord2:

      j3 ≤ j ==> Ord(j)

lemmas le_Ord2:

      j3 ≤ j ==> Ord(j)

lemmas lt0E:

      i1 < 0 ==> R

lemmas lt0E:

      i1 < 0 ==> R

lemma lt_trans:

      [| i < j; j < k |] ==> i < k

lemma lt_not_sym:

      i < j ==> ¬ j < i

lemmas lt_asym:

      [| i1 < j1; ¬ P ==> j1 < i1 |] ==> P

lemmas lt_asym:

      [| i1 < j1; ¬ P ==> j1 < i1 |] ==> P

lemma lt_irrefl:

      i < i ==> P

lemma lt_not_refl:

      ¬ i < i

lemma le_iff:

      i ≤ j <-> i < j ∨ i = j ∧ Ord(j)

lemma leI:

      i < j ==> i ≤ j

lemma le_eqI:

      [| i = j; Ord(j) |] ==> i ≤ j

lemmas le_refl:

      Ord(i) ==> i ≤ i

lemmas le_refl:

      Ord(i) ==> i ≤ i

lemma le_refl_iff:

      i ≤ i <-> Ord(i)

lemma leCI:

      (¬ (i = j ∧ Ord(j)) ==> i < j) ==> i ≤ j

lemma leE:

      [| i ≤ j; i < j ==> P; [| i = j; Ord(j) |] ==> P |] ==> P

lemma le_anti_sym:

      [| i ≤ j; j ≤ i |] ==> i = j

lemma le0_iff:

      i ≤ 0 <-> i = 0

lemmas le0D:

      i1 ≤ 0 ==> i1 = 0

lemmas le0D:

      i1 ≤ 0 ==> i1 = 0

### Natural Deduction Rules for Memrel

lemma Memrel_iff:

      ⟨a, b⟩ ∈ Memrel(A) <-> a ∈ b ∧ a ∈ A ∧ b ∈ A

lemma MemrelI:

      [| a ∈ b; a ∈ A; b ∈ A |] ==> ⟨a, b⟩ ∈ Memrel(A)

lemma MemrelE:

      [| ⟨a, b⟩ ∈ Memrel(A); [| a ∈ A; b ∈ A; a ∈ b |] ==> P |] ==> P

lemma Memrel_type:

      Memrel(A) ⊆ A × A

lemma Memrel_mono:

      A ⊆ B ==> Memrel(A) ⊆ Memrel(B)

lemma Memrel_0:

      Memrel(0) = 0

lemma Memrel_1:

      Memrel(1) = 0

lemma relation_Memrel:

      relation(Memrel(A))

lemma wf_Memrel:

      wf(Memrel(A))

lemma trans_Memrel:

      Ord(i) ==> trans(Memrel(i))

lemma Transset_trans_Memrel:

      ∀j∈i. Transset(j) ==> trans(Memrel(i))

lemma Transset_Memrel_iff:

      Transset(A) ==> ⟨a, b⟩ ∈ Memrel(A) <-> a ∈ b ∧ b ∈ A

### Transfinite Induction

lemma Transset_induct:

      [| i ∈ k; Transset(k); !!x. [| x ∈ k; ∀y∈x. P(y) |] ==> P(x) |] ==> P(i)

lemmas Ord_induct:

      [| i ∈ k; Ord(k); !!x. [| x ∈ k; ∀y∈x. P(y) |] ==> P(x) |] ==> P(i)

lemmas Ord_induct:

      [| i ∈ k; Ord(k); !!x. [| x ∈ k; ∀y∈x. P(y) |] ==> P(x) |] ==> P(i)

lemmas Ord_induct_rule:

      [| i ∈ k; Ord(k); !!x. [| x ∈ k; !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |] ==> P(i)

lemmas Ord_induct_rule:

      [| i ∈ k; Ord(k); !!x. [| x ∈ k; !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |] ==> P(i)

lemma trans_induct:

      [| Ord(i); !!x. [| Ord(x); ∀y∈x. P(y) |] ==> P(x) |] ==> P(i)

lemmas trans_induct_rule:

      [| Ord(i); !!x. [| Ord(x); !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |] ==> P(i)

lemmas trans_induct_rule:

      [| Ord(i); !!x. [| Ord(x); !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |] ==> P(i)

#### Proving That < is a Linear Ordering on the Ordinals

lemma Ord_linear:

      [| Ord(i); Ord(j) |] ==> i ∈ j ∨ i = j ∨ j ∈ i

lemma Ord_linear_lt:

      [| Ord(i); Ord(j); i < j ==> P; i = j ==> P; j < i ==> P |] ==> P

lemma Ord_linear2:

      [| Ord(i); Ord(j); i < j ==> P; j ≤ i ==> P |] ==> P

lemma Ord_linear_le:

      [| Ord(i); Ord(j); i ≤ j ==> P; j ≤ i ==> P |] ==> P

lemma le_imp_not_lt:

      j ≤ i ==> ¬ i < j

lemma not_lt_imp_le:

      [| ¬ i < j; Ord(i); Ord(j) |] ==> j ≤ i

#### Some Rewrite Rules for <, le

lemma Ord_mem_iff_lt:

      Ord(j) ==> i ∈ j <-> i < j

lemma not_lt_iff_le:

      [| Ord(i); Ord(j) |] ==> ¬ i < j <-> j ≤ i

lemma not_le_iff_lt:

      [| Ord(i); Ord(j) |] ==> ¬ i ≤ j <-> j < i

lemma Ord_0_le:

      Ord(i) ==> 0 ≤ i

lemma Ord_0_lt:

      [| Ord(i); i ≠ 0 |] ==> 0 < i

lemma Ord_0_lt_iff:

      Ord(i) ==> i ≠ 0 <-> 0 < i

### Results about Less-Than or Equals

lemma zero_le_succ_iff:

      0 ≤ succ(x) <-> Ord(x)

lemma subset_imp_le:

      [| j ⊆ i; Ord(i); Ord(j) |] ==> j ≤ i

lemma le_imp_subset:

      i ≤ j ==> i ⊆ j

lemma le_subset_iff:

      j ≤ i <-> j ⊆ i ∧ Ord(i) ∧ Ord(j)

lemma le_succ_iff:

      i ≤ succ(j) <-> i ≤ j ∨ i = succ(j) ∧ Ord(i)

lemma all_lt_imp_le:

      [| Ord(i); Ord(j); !!x. x < j ==> x < i |] ==> j ≤ i

#### Transitivity Laws

lemma lt_trans1:

      [| i ≤ j; j < k |] ==> i < k

lemma lt_trans2:

      [| i < j; j ≤ k |] ==> i < k

lemma le_trans:

      [| i ≤ j; j ≤ k |] ==> i ≤ k

lemma succ_leI:

      i < j ==> succ(i) ≤ j

lemma succ_leE:

      succ(i) ≤ j ==> i < j

lemma succ_le_iff:

      succ(i) ≤ j <-> i < j

lemma succ_le_imp_le:

      succ(i) ≤ succ(j) ==> i ≤ j

lemma lt_subset_trans:

      [| i ⊆ j; j < k; Ord(i) |] ==> i < k

lemma lt_imp_0_lt:

      j < i ==> 0 < i

lemma succ_lt_iff:

      succ(i) < j <-> i < j ∧ succ(i) ≠ j

lemma Ord_succ_mem_iff:

      Ord(j) ==> succ(i) ∈ succ(j) <-> i ∈ j

#### Union and Intersection

lemma Un_upper1_le:

      [| Ord(i); Ord(j) |] ==> i ≤ i ∪ j

lemma Un_upper2_le:

      [| Ord(i); Ord(j) |] ==> j ≤ i ∪ j

lemma Un_least_lt:

      [| i < k; j < k |] ==> i ∪ j < k

lemma Un_least_lt_iff:

      [| Ord(i); Ord(j) |] ==> i ∪ j < k <-> i < k ∧ j < k

lemma Un_least_mem_iff:

      [| Ord(i); Ord(j); Ord(k) |] ==> i ∪ j ∈ k <-> i ∈ k ∧ j ∈ k

lemma Int_greatest_lt:

      [| i < k; j < k |] ==> i ∩ j < k

lemma Ord_Un_if:

      [| Ord(i); Ord(j) |] ==> i ∪ j = (if j < i then i else j)

lemma succ_Un_distrib:

      [| Ord(i); Ord(j) |] ==> succ(i ∪ j) = succ(i) ∪ succ(j)

lemma lt_Un_iff:

      [| Ord(i); Ord(j) |] ==> k < i ∪ j <-> k < i ∨ k < j

lemma le_Un_iff:

      [| Ord(i); Ord(j) |] ==> k ≤ i ∪ j <-> k ≤ i ∨ k ≤ j

lemma Un_upper1_lt:

      [| k < i; Ord(j) |] ==> k < i ∪ j

lemma Un_upper2_lt:

      [| k < j; Ord(i) |] ==> k < i ∪ j

lemma Ord_Union_succ_eq:

      Ord(i) ==> \<Union>succ(i) = i

### Results about Limits

lemma Ord_Union:

      (!!i. i ∈ A ==> Ord(i)) ==> Ord(\<Union>A)

lemma Ord_UN:

      (!!x. x ∈ A ==> Ord(B(x))) ==> Ord(\<Union>x∈A. B(x))

lemma Ord_Inter:

      (!!i. i ∈ A ==> Ord(i)) ==> Ord(\<Inter>A)

lemma Ord_INT:

      (!!x. x ∈ A ==> Ord(B(x))) ==> Ord(\<Inter>x∈A. B(x))

lemma UN_least_le:

      [| Ord(i); !!x. x ∈ A ==> b(x) ≤ i |] ==> (\<Union>x∈A. b(x)) ≤ i

lemma UN_succ_least_lt:

      [| j < i; !!x. x ∈ A ==> b(x) < j |] ==> (\<Union>x∈A. succ(b(x))) < i

lemma UN_upper_lt:

      [| a ∈ A; i < b(a); Ord(\<Union>x∈A. b(x)) |] ==> i < (\<Union>x∈A. b(x))

lemma UN_upper_le:

      [| a ∈ A; i ≤ b(a); Ord(\<Union>x∈A. b(x)) |] ==> i ≤ (\<Union>x∈A. b(x))

lemma lt_Union_iff:

      ∀i∈A. Ord(i) ==> j < \<Union>A <-> (∃i∈A. j < i)

lemma Union_upper_le:

      [| j ∈ J; i ≤ j; Ord(\<Union>J) |] ==> i ≤ \<Union>J

lemma le_implies_UN_le_UN:

      (!!x. x ∈ A ==> c(x) ≤ d(x)) ==> (\<Union>x∈A. c(x)) ≤ (\<Union>x∈A. d(x))

lemma Ord_equality:

      Ord(i) ==> (\<Union>y∈i. succ(y)) = i

lemma Ord_Union_subset:

      Ord(i) ==> \<Union>i ⊆ i

### Limit Ordinals -- General Properties

lemma Limit_Union_eq:

      Limit(i) ==> \<Union>i = i

lemma Limit_is_Ord:

      Limit(i) ==> Ord(i)

lemma Limit_has_0:

      Limit(i) ==> 0 < i

lemma Limit_nonzero:

      Limit(i) ==> i ≠ 0

lemma Limit_has_succ:

      [| Limit(i); j < i |] ==> succ(j) < i

lemma Limit_succ_lt_iff:

      Limit(i) ==> succ(j) < i <-> j < i

lemma zero_not_Limit:

      ¬ Limit(0)

lemma Limit_has_1:

      Limit(i) ==> 1 < i

lemma increasing_LimitI:

      [| 0 < l; ∀x∈l. ∃y∈l. x < y |] ==> Limit(l)

lemma non_succ_LimitI:

      [| 0 < i; ∀y. succ(y) ≠ i |] ==> Limit(i)

lemma succ_LimitE:

      Limit(succ(i)) ==> P

lemma not_succ_Limit:

      ¬ Limit(succ(i))

lemma Limit_le_succD:

      [| Limit(i); i ≤ succ(j) |] ==> i ≤ j

#### Traditional 3-Way Case Analysis on Ordinals

lemma Ord_cases_disj:

      Ord(i) ==> i = 0 ∨ (∃j. Ord(j) ∧ i = succ(j)) ∨ Limit(i)

lemma Ord_cases:

      [| Ord(i); i = 0 ==> P; !!j. [| Ord(j); i = succ(j) |] ==> P; Limit(i) ==> P |]
      ==> P

lemma trans_induct3:

      [| Ord(i); P(0); !!x. [| Ord(x); P(x) |] ==> P(succ(x));
         !!x. [| Limit(x); ∀y∈x. P(y) |] ==> P(x) |]
      ==> P(i)

lemmas trans_induct3_rule:

      [| Ord(i); P(0); !!x. [| Ord(x); P(x) |] ==> P(succ(x));
         !!x. [| Limit(x); !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |]
      ==> P(i)

lemmas trans_induct3_rule:

      [| Ord(i); P(0); !!x. [| Ord(x); P(x) |] ==> P(succ(x));
         !!x. [| Limit(x); !!xa. xa ∈ x ==> P(xa) |] ==> P(x) |]
      ==> P(i)

lemma Ord_set_cases:

      ∀i∈I. Ord(i) ==> I = 0 ∨ \<Union>I ∈ I ∨ \<Union>I ∉ I ∧ Limit(\<Union>I)

lemma Ord_Union_eq_succD:

      [| ∀x∈X. Ord(x); \<Union>X = succ(j) |] ==> succ(j) ∈ X

lemma Limit_Union:

      [| I ≠ 0; !!x. x ∈ I ==> Limit(x) |] ==> Limit(\<Union>I)