Theory CardinalArith (Isabelle2005: October 2005)

# Theory CardinalArith

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theory CardinalArith
imports Cardinal OrderArith ArithSimp Finite
begin

    (*  Title:      ZF/CardinalArith.thy
        ID:         $Id: CardinalArith.thy,v 1.31 2005/06/17 14:15:09 haftmann Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1994  University of Cambridge

    *)

    header{*Cardinal Arithmetic Without the Axiom of Choice*}

    theory CardinalArith imports Cardinal OrderArith ArithSimp Finite begin

    constdefs

      InfCard       :: "i=>o"
        "InfCard(i) == Card(i) & nat le i"

      cmult         :: "[i,i]=>i"       (infixl "|*|" 70)
        "i |*| j == |i*j|"

      cadd          :: "[i,i]=>i"       (infixl "|+|" 65)
        "i |+| j == |i+j|"

      csquare_rel   :: "i=>i"
        "csquare_rel(K) ==
              rvimage(K*K,
                      lam <x,y>:K*K. <x Un y, x, y>,
                      rmult(K,Memrel(K), K*K, rmult(K,Memrel(K), K,Memrel(K))))"

      jump_cardinal :: "i=>i"
        --{*This def is more complex than Kunen's but it more easily proved to
            be a cardinal*}
        "jump_cardinal(K) ==
             \<Union>X∈Pow(K). {z. r: Pow(K*K), well_ord(X,r) & z = ordertype(X,r)}"

      csucc         :: "i=>i"
        --{*needed because @{term "jump_cardinal(K)"} might not be the successor
            of @{term K}*}
        "csucc(K) == LEAST L. Card(L) & K<L"

    syntax (xsymbols)
      "op |+|"     :: "[i,i] => i"          (infixl "⊕" 65)
      "op |*|"     :: "[i,i] => i"          (infixl "⊗" 70)
    syntax (HTML output)
      "op |+|"     :: "[i,i] => i"          (infixl "⊕" 65)
      "op |*|"     :: "[i,i] => i"          (infixl "⊗" 70)

    lemma Card_Union [simp,intro,TC]: "(ALL x:A. Card(x)) ==> Card(Union(A))"
    apply (rule CardI)
     apply (simp add: Card_is_Ord)
    apply (clarify dest!: ltD)
    apply (drule bspec, assumption)
    apply (frule lt_Card_imp_lesspoll, blast intro: ltI Card_is_Ord)
    apply (drule eqpoll_sym [THEN eqpoll_imp_lepoll])
    apply (drule lesspoll_trans1, assumption)
    apply (subgoal_tac "B \<lesssim> \<Union>A")
     apply (drule lesspoll_trans1, assumption, blast)
    apply (blast intro: subset_imp_lepoll)
    done

    lemma Card_UN: "(!!x. x:A ==> Card(K(x))) ==> Card(\<Union>x∈A. K(x))"
    by (blast intro: Card_Union)

    lemma Card_OUN [simp,intro,TC]:
         "(!!x. x:A ==> Card(K(x))) ==> Card(\<Union>x<A. K(x))"
    by (simp add: OUnion_def Card_0)

    lemma n_lesspoll_nat: "n ∈ nat ==> n \<prec> nat"
    apply (unfold lesspoll_def)
    apply (rule conjI)
    apply (erule OrdmemD [THEN subset_imp_lepoll], rule Ord_nat)
    apply (rule notI)
    apply (erule eqpollE)
    apply (rule succ_lepoll_natE)
    apply (blast intro: nat_succI [THEN OrdmemD, THEN subset_imp_lepoll]
                        lepoll_trans, assumption)
    done

    lemma in_Card_imp_lesspoll: "[| Card(K); b ∈ K |] ==> b \<prec> K"
    apply (unfold lesspoll_def)
    apply (simp add: Card_iff_initial)
    apply (fast intro!: le_imp_lepoll ltI leI)
    done

    lemma lesspoll_lemma: "[| ~ A \<prec> B; C \<prec> B |] ==> A - C ≠ 0"
    apply (unfold lesspoll_def)
    apply (fast dest!: Diff_eq_0_iff [THEN iffD1, THEN subset_imp_lepoll]
                intro!: eqpollI elim: notE
                elim!: eqpollE lepoll_trans)
    done

    subsection{*Cardinal addition*}

    text{*Note: Could omit proving the algebraic laws for cardinal addition and
    multiplication.  On finite cardinals these operations coincide with
    addition and multiplication of natural numbers; on infinite cardinals they
    coincide with union (maximum).  Either way we get most laws for free.*}

    subsubsection{*Cardinal addition is commutative*}

    lemma sum_commute_eqpoll: "A+B ≈ B+A"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule_tac c = "case(Inr,Inl)" and d = "case(Inr,Inl)" in lam_bijective)
    apply auto
    done

    lemma cadd_commute: "i |+| j = j |+| i"
    apply (unfold cadd_def)
    apply (rule sum_commute_eqpoll [THEN cardinal_cong])
    done

    subsubsection{*Cardinal addition is associative*}

    lemma sum_assoc_eqpoll: "(A+B)+C ≈ A+(B+C)"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule sum_assoc_bij)
    done

    (*Unconditional version requires AC*)
    lemma well_ord_cadd_assoc:
        "[| well_ord(i,ri); well_ord(j,rj); well_ord(k,rk) |]
         ==> (i |+| j) |+| k = i |+| (j |+| k)"
    apply (unfold cadd_def)
    apply (rule cardinal_cong)
    apply (rule eqpoll_trans)
     apply (rule sum_eqpoll_cong [OF well_ord_cardinal_eqpoll eqpoll_refl])
     apply (blast intro: well_ord_radd )
    apply (rule sum_assoc_eqpoll [THEN eqpoll_trans])
    apply (rule eqpoll_sym)
    apply (rule sum_eqpoll_cong [OF eqpoll_refl well_ord_cardinal_eqpoll])
    apply (blast intro: well_ord_radd )
    done

    subsubsection{*0 is the identity for addition*}

    lemma sum_0_eqpoll: "0+A ≈ A"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule bij_0_sum)
    done

    lemma cadd_0 [simp]: "Card(K) ==> 0 |+| K = K"
    apply (unfold cadd_def)
    apply (simp add: sum_0_eqpoll [THEN cardinal_cong] Card_cardinal_eq)
    done

    subsubsection{*Addition by another cardinal*}

    lemma sum_lepoll_self: "A \<lesssim> A+B"
    apply (unfold lepoll_def inj_def)
    apply (rule_tac x = "lam x:A. Inl (x) " in exI)
    apply simp
    done

    (*Could probably weaken the premises to well_ord(K,r), or removing using AC*)

    lemma cadd_le_self:
        "[| Card(K);  Ord(L) |] ==> K le (K |+| L)"
    apply (unfold cadd_def)
    apply (rule le_trans [OF Card_cardinal_le well_ord_lepoll_imp_Card_le],
           assumption)
    apply (rule_tac [2] sum_lepoll_self)
    apply (blast intro: well_ord_radd well_ord_Memrel Card_is_Ord)
    done

    subsubsection{*Monotonicity of addition*}

    lemma sum_lepoll_mono:
         "[| A \<lesssim> C;  B \<lesssim> D |] ==> A + B \<lesssim> C + D"
    apply (unfold lepoll_def)
    apply (elim exE)
    apply (rule_tac x = "lam z:A+B. case (%w. Inl(f`w), %y. Inr(fa`y), z)" in exI)
    apply (rule_tac d = "case (%w. Inl(converse(f) `w), %y. Inr(converse(fa) ` y))"
           in lam_injective)
    apply (typecheck add: inj_is_fun, auto)
    done

    lemma cadd_le_mono:
        "[| K' le K;  L' le L |] ==> (K' |+| L') le (K |+| L)"
    apply (unfold cadd_def)
    apply (safe dest!: le_subset_iff [THEN iffD1])
    apply (rule well_ord_lepoll_imp_Card_le)
    apply (blast intro: well_ord_radd well_ord_Memrel)
    apply (blast intro: sum_lepoll_mono subset_imp_lepoll)
    done

    subsubsection{*Addition of finite cardinals is "ordinary" addition*}

    lemma sum_succ_eqpoll: "succ(A)+B ≈ succ(A+B)"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule_tac c = "%z. if z=Inl (A) then A+B else z"
                and d = "%z. if z=A+B then Inl (A) else z" in lam_bijective)
       apply simp_all
    apply (blast dest: sym [THEN eq_imp_not_mem] elim: mem_irrefl)+
    done

    (*Pulling the  succ(...)  outside the |...| requires m, n: nat  *)
    (*Unconditional version requires AC*)
    lemma cadd_succ_lemma:
        "[| Ord(m);  Ord(n) |] ==> succ(m) |+| n = |succ(m |+| n)|"
    apply (unfold cadd_def)
    apply (rule sum_succ_eqpoll [THEN cardinal_cong, THEN trans])
    apply (rule succ_eqpoll_cong [THEN cardinal_cong])
    apply (rule well_ord_cardinal_eqpoll [THEN eqpoll_sym])
    apply (blast intro: well_ord_radd well_ord_Memrel)
    done

    lemma nat_cadd_eq_add: "[| m: nat;  n: nat |] ==> m |+| n = m#+n"
    apply (induct_tac m)
    apply (simp add: nat_into_Card [THEN cadd_0])
    apply (simp add: cadd_succ_lemma nat_into_Card [THEN Card_cardinal_eq])
    done

    subsection{*Cardinal multiplication*}

    subsubsection{*Cardinal multiplication is commutative*}

    (*Easier to prove the two directions separately*)
    lemma prod_commute_eqpoll: "A*B ≈ B*A"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule_tac c = "%<x,y>.<y,x>" and d = "%<x,y>.<y,x>" in lam_bijective,
           auto)
    done

    lemma cmult_commute: "i |*| j = j |*| i"
    apply (unfold cmult_def)
    apply (rule prod_commute_eqpoll [THEN cardinal_cong])
    done

    subsubsection{*Cardinal multiplication is associative*}

    lemma prod_assoc_eqpoll: "(A*B)*C ≈ A*(B*C)"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule prod_assoc_bij)
    done

    (*Unconditional version requires AC*)
    lemma well_ord_cmult_assoc:
        "[| well_ord(i,ri); well_ord(j,rj); well_ord(k,rk) |]
         ==> (i |*| j) |*| k = i |*| (j |*| k)"
    apply (unfold cmult_def)
    apply (rule cardinal_cong)
    apply (rule eqpoll_trans)
     apply (rule prod_eqpoll_cong [OF well_ord_cardinal_eqpoll eqpoll_refl])
     apply (blast intro: well_ord_rmult)
    apply (rule prod_assoc_eqpoll [THEN eqpoll_trans])
    apply (rule eqpoll_sym)
    apply (rule prod_eqpoll_cong [OF eqpoll_refl well_ord_cardinal_eqpoll])
    apply (blast intro: well_ord_rmult)
    done

    subsubsection{*Cardinal multiplication distributes over addition*}

    lemma sum_prod_distrib_eqpoll: "(A+B)*C ≈ (A*C)+(B*C)"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule sum_prod_distrib_bij)
    done

    lemma well_ord_cadd_cmult_distrib:
        "[| well_ord(i,ri); well_ord(j,rj); well_ord(k,rk) |]
         ==> (i |+| j) |*| k = (i |*| k) |+| (j |*| k)"
    apply (unfold cadd_def cmult_def)
    apply (rule cardinal_cong)
    apply (rule eqpoll_trans)
     apply (rule prod_eqpoll_cong [OF well_ord_cardinal_eqpoll eqpoll_refl])
    apply (blast intro: well_ord_radd)
    apply (rule sum_prod_distrib_eqpoll [THEN eqpoll_trans])
    apply (rule eqpoll_sym)
    apply (rule sum_eqpoll_cong [OF well_ord_cardinal_eqpoll
                                    well_ord_cardinal_eqpoll])
    apply (blast intro: well_ord_rmult)+
    done

    subsubsection{*Multiplication by 0 yields 0*}

    lemma prod_0_eqpoll: "0*A ≈ 0"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule lam_bijective, safe)
    done

    lemma cmult_0 [simp]: "0 |*| i = 0"
    by (simp add: cmult_def prod_0_eqpoll [THEN cardinal_cong])

    subsubsection{*1 is the identity for multiplication*}

    lemma prod_singleton_eqpoll: "{x}*A ≈ A"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule singleton_prod_bij [THEN bij_converse_bij])
    done

    lemma cmult_1 [simp]: "Card(K) ==> 1 |*| K = K"
    apply (unfold cmult_def succ_def)
    apply (simp add: prod_singleton_eqpoll [THEN cardinal_cong] Card_cardinal_eq)
    done

    subsection{*Some inequalities for multiplication*}

    lemma prod_square_lepoll: "A \<lesssim> A*A"
    apply (unfold lepoll_def inj_def)
    apply (rule_tac x = "lam x:A. <x,x>" in exI, simp)
    done

    (*Could probably weaken the premise to well_ord(K,r), or remove using AC*)
    lemma cmult_square_le: "Card(K) ==> K le K |*| K"
    apply (unfold cmult_def)
    apply (rule le_trans)
    apply (rule_tac [2] well_ord_lepoll_imp_Card_le)
    apply (rule_tac [3] prod_square_lepoll)
    apply (simp add: le_refl Card_is_Ord Card_cardinal_eq)
    apply (blast intro: well_ord_rmult well_ord_Memrel Card_is_Ord)
    done

    subsubsection{*Multiplication by a non-zero cardinal*}

    lemma prod_lepoll_self: "b: B ==> A \<lesssim> A*B"
    apply (unfold lepoll_def inj_def)
    apply (rule_tac x = "lam x:A. <x,b>" in exI, simp)
    done

    (*Could probably weaken the premises to well_ord(K,r), or removing using AC*)
    lemma cmult_le_self:
        "[| Card(K);  Ord(L);  0<L |] ==> K le (K |*| L)"
    apply (unfold cmult_def)
    apply (rule le_trans [OF Card_cardinal_le well_ord_lepoll_imp_Card_le])
      apply assumption
     apply (blast intro: well_ord_rmult well_ord_Memrel Card_is_Ord)
    apply (blast intro: prod_lepoll_self ltD)
    done

    subsubsection{*Monotonicity of multiplication*}

    lemma prod_lepoll_mono:
         "[| A \<lesssim> C;  B \<lesssim> D |] ==> A * B  \<lesssim>  C * D"
    apply (unfold lepoll_def)
    apply (elim exE)
    apply (rule_tac x = "lam <w,y>:A*B. <f`w, fa`y>" in exI)
    apply (rule_tac d = "%<w,y>. <converse (f) `w, converse (fa) `y>"
           in lam_injective)
    apply (typecheck add: inj_is_fun, auto)
    done

    lemma cmult_le_mono:
        "[| K' le K;  L' le L |] ==> (K' |*| L') le (K |*| L)"
    apply (unfold cmult_def)
    apply (safe dest!: le_subset_iff [THEN iffD1])
    apply (rule well_ord_lepoll_imp_Card_le)
     apply (blast intro: well_ord_rmult well_ord_Memrel)
    apply (blast intro: prod_lepoll_mono subset_imp_lepoll)
    done

    subsection{*Multiplication of finite cardinals is "ordinary" multiplication*}

    lemma prod_succ_eqpoll: "succ(A)*B ≈ B + A*B"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (rule_tac c = "%<x,y>. if x=A then Inl (y) else Inr (<x,y>)"
                and d = "case (%y. <A,y>, %z. z)" in lam_bijective)
    apply safe
    apply (simp_all add: succI2 if_type mem_imp_not_eq)
    done

    (*Unconditional version requires AC*)
    lemma cmult_succ_lemma:
        "[| Ord(m);  Ord(n) |] ==> succ(m) |*| n = n |+| (m |*| n)"
    apply (unfold cmult_def cadd_def)
    apply (rule prod_succ_eqpoll [THEN cardinal_cong, THEN trans])
    apply (rule cardinal_cong [symmetric])
    apply (rule sum_eqpoll_cong [OF eqpoll_refl well_ord_cardinal_eqpoll])
    apply (blast intro: well_ord_rmult well_ord_Memrel)
    done

    lemma nat_cmult_eq_mult: "[| m: nat;  n: nat |] ==> m |*| n = m#*n"
    apply (induct_tac m)
    apply (simp_all add: cmult_succ_lemma nat_cadd_eq_add)
    done

    lemma cmult_2: "Card(n) ==> 2 |*| n = n |+| n"
    by (simp add: cmult_succ_lemma Card_is_Ord cadd_commute [of _ 0])

    lemma sum_lepoll_prod: "2 \<lesssim> C ==> B+B \<lesssim> C*B"
    apply (rule lepoll_trans)
    apply (rule sum_eq_2_times [THEN equalityD1, THEN subset_imp_lepoll])
    apply (erule prod_lepoll_mono)
    apply (rule lepoll_refl)
    done

    lemma lepoll_imp_sum_lepoll_prod: "[| A \<lesssim> B; 2 \<lesssim> A |] ==> A+B \<lesssim> A*B"
    by (blast intro: sum_lepoll_mono sum_lepoll_prod lepoll_trans lepoll_refl)

    subsection{*Infinite Cardinals are Limit Ordinals*}

    (*This proof is modelled upon one assuming nat<=A, with injection
      lam z:cons(u,A). if z=u then 0 else if z : nat then succ(z) else z
      and inverse %y. if y:nat then nat_case(u, %z. z, y) else y.  \
      If f: inj(nat,A) then range(f) behaves like the natural numbers.*)
    lemma nat_cons_lepoll: "nat \<lesssim> A ==> cons(u,A) \<lesssim> A"
    apply (unfold lepoll_def)
    apply (erule exE)
    apply (rule_tac x =
              "lam z:cons (u,A).
                 if z=u then f`0
                 else if z: range (f) then f`succ (converse (f) `z) else z"
           in exI)
    apply (rule_tac d =
              "%y. if y: range(f) then nat_case (u, %z. f`z, converse(f) `y)
                                  else y"
           in lam_injective)
    apply (fast intro!: if_type apply_type intro: inj_is_fun inj_converse_fun)
    apply (simp add: inj_is_fun [THEN apply_rangeI]
                     inj_converse_fun [THEN apply_rangeI]
                     inj_converse_fun [THEN apply_funtype])
    done

    lemma nat_cons_eqpoll: "nat \<lesssim> A ==> cons(u,A) ≈ A"
    apply (erule nat_cons_lepoll [THEN eqpollI])
    apply (rule subset_consI [THEN subset_imp_lepoll])
    done

    (*Specialized version required below*)
    lemma nat_succ_eqpoll: "nat <= A ==> succ(A) ≈ A"
    apply (unfold succ_def)
    apply (erule subset_imp_lepoll [THEN nat_cons_eqpoll])
    done

    lemma InfCard_nat: "InfCard(nat)"
    apply (unfold InfCard_def)
    apply (blast intro: Card_nat le_refl Card_is_Ord)
    done

    lemma InfCard_is_Card: "InfCard(K) ==> Card(K)"
    apply (unfold InfCard_def)
    apply (erule conjunct1)
    done

    lemma InfCard_Un:
        "[| InfCard(K);  Card(L) |] ==> InfCard(K Un L)"
    apply (unfold InfCard_def)
    apply (simp add: Card_Un Un_upper1_le [THEN [2] le_trans]  Card_is_Ord)
    done

    (*Kunen's Lemma 10.11*)
    lemma InfCard_is_Limit: "InfCard(K) ==> Limit(K)"
    apply (unfold InfCard_def)
    apply (erule conjE)
    apply (frule Card_is_Ord)
    apply (rule ltI [THEN non_succ_LimitI])
    apply (erule le_imp_subset [THEN subsetD])
    apply (safe dest!: Limit_nat [THEN Limit_le_succD])
    apply (unfold Card_def)
    apply (drule trans)
    apply (erule le_imp_subset [THEN nat_succ_eqpoll, THEN cardinal_cong])
    apply (erule Ord_cardinal_le [THEN lt_trans2, THEN lt_irrefl])
    apply (rule le_eqI, assumption)
    apply (rule Ord_cardinal)
    done

    (*** An infinite cardinal equals its square (Kunen, Thm 10.12, page 29) ***)

    (*A general fact about ordermap*)
    lemma ordermap_eqpoll_pred:
        "[| well_ord(A,r);  x:A |] ==> ordermap(A,r)`x ≈ Order.pred(A,x,r)"
    apply (unfold eqpoll_def)
    apply (rule exI)
    apply (simp add: ordermap_eq_image well_ord_is_wf)
    apply (erule ordermap_bij [THEN bij_is_inj, THEN restrict_bij,
                               THEN bij_converse_bij])
    apply (rule pred_subset)
    done

    subsubsection{*Establishing the well-ordering*}

    lemma csquare_lam_inj:
         "Ord(K) ==> (lam <x,y>:K*K. <x Un y, x, y>) : inj(K*K, K*K*K)"
    apply (unfold inj_def)
    apply (force intro: lam_type Un_least_lt [THEN ltD] ltI)
    done

    lemma well_ord_csquare: "Ord(K) ==> well_ord(K*K, csquare_rel(K))"
    apply (unfold csquare_rel_def)
    apply (rule csquare_lam_inj [THEN well_ord_rvimage], assumption)
    apply (blast intro: well_ord_rmult well_ord_Memrel)
    done

    subsubsection{*Characterising initial segments of the well-ordering*}

    lemma csquareD:
     "[| <<x,y>, <z,z>> : csquare_rel(K);  x<K;  y<K;  z<K |] ==> x le z & y le z"
    apply (unfold csquare_rel_def)
    apply (erule rev_mp)
    apply (elim ltE)
    apply (simp add: rvimage_iff Un_absorb Un_least_mem_iff ltD)
    apply (safe elim!: mem_irrefl intro!: Un_upper1_le Un_upper2_le)
    apply (simp_all add: lt_def succI2)
    done

    lemma pred_csquare_subset:
        "z<K ==> Order.pred(K*K, <z,z>, csquare_rel(K)) <= succ(z)*succ(z)"
    apply (unfold Order.pred_def)
    apply (safe del: SigmaI succCI)
    apply (erule csquareD [THEN conjE])
    apply (unfold lt_def, auto)
    done

    lemma csquare_ltI:
     "[| x<z;  y<z;  z<K |] ==>  <<x,y>, <z,z>> : csquare_rel(K)"
    apply (unfold csquare_rel_def)
    apply (subgoal_tac "x<K & y<K")
     prefer 2 apply (blast intro: lt_trans)
    apply (elim ltE)
    apply (simp add: rvimage_iff Un_absorb Un_least_mem_iff ltD)
    done

    (*Part of the traditional proof.  UNUSED since it's harder to prove & apply *)
    lemma csquare_or_eqI:
     "[| x le z;  y le z;  z<K |] ==> <<x,y>, <z,z>> : csquare_rel(K) | x=z & y=z"
    apply (unfold csquare_rel_def)
    apply (subgoal_tac "x<K & y<K")
     prefer 2 apply (blast intro: lt_trans1)
    apply (elim ltE)
    apply (simp add: rvimage_iff Un_absorb Un_least_mem_iff ltD)
    apply (elim succE)
    apply (simp_all add: subset_Un_iff [THEN iff_sym]
                         subset_Un_iff2 [THEN iff_sym] OrdmemD)
    done

    subsubsection{*The cardinality of initial segments*}

    lemma ordermap_z_lt:
          "[| Limit(K);  x<K;  y<K;  z=succ(x Un y) |] ==>
              ordermap(K*K, csquare_rel(K)) ` <x,y> <
              ordermap(K*K, csquare_rel(K)) ` <z,z>"
    apply (subgoal_tac "z<K & well_ord (K*K, csquare_rel (K))")
    prefer 2 apply (blast intro!: Un_least_lt Limit_has_succ
                                  Limit_is_Ord [THEN well_ord_csquare], clarify)
    apply (rule csquare_ltI [THEN ordermap_mono, THEN ltI])
    apply (erule_tac [4] well_ord_is_wf)
    apply (blast intro!: Un_upper1_le Un_upper2_le Ord_ordermap elim!: ltE)+
    done

    (*Kunen: "each <x,y>: K*K has no more than z*z predecessors..." (page 29) *)
    lemma ordermap_csquare_le:
      "[| Limit(K);  x<K;  y<K;  z=succ(x Un y) |]
       ==> | ordermap(K*K, csquare_rel(K)) ` <x,y> | le  |succ(z)| |*| |succ(z)|"
    apply (unfold cmult_def)
    apply (rule well_ord_rmult [THEN well_ord_lepoll_imp_Card_le])
    apply (rule Ord_cardinal [THEN well_ord_Memrel])+
    apply (subgoal_tac "z<K")
     prefer 2 apply (blast intro!: Un_least_lt Limit_has_succ)
    apply (rule ordermap_z_lt [THEN leI, THEN le_imp_lepoll, THEN lepoll_trans],
           assumption+)
    apply (rule ordermap_eqpoll_pred [THEN eqpoll_imp_lepoll, THEN lepoll_trans])
    apply (erule Limit_is_Ord [THEN well_ord_csquare])
    apply (blast intro: ltD)
    apply (rule pred_csquare_subset [THEN subset_imp_lepoll, THEN lepoll_trans],
                assumption)
    apply (elim ltE)
    apply (rule prod_eqpoll_cong [THEN eqpoll_sym, THEN eqpoll_imp_lepoll])
    apply (erule Ord_succ [THEN Ord_cardinal_eqpoll])+
    done

    (*Kunen: "... so the order type <= K" *)
    lemma ordertype_csquare_le:
         "[| InfCard(K);  ALL y:K. InfCard(y) --> y |*| y = y |]
          ==> ordertype(K*K, csquare_rel(K)) le K"
    apply (frule InfCard_is_Card [THEN Card_is_Ord])
    apply (rule all_lt_imp_le, assumption)
    apply (erule well_ord_csquare [THEN Ord_ordertype])
    apply (rule Card_lt_imp_lt)
    apply (erule_tac [3] InfCard_is_Card)
    apply (erule_tac [2] ltE)
    apply (simp add: ordertype_unfold)
    apply (safe elim!: ltE)
    apply (subgoal_tac "Ord (xa) & Ord (ya)")
     prefer 2 apply (blast intro: Ord_in_Ord, clarify)
    (*??WHAT A MESS!*)
    apply (rule InfCard_is_Limit [THEN ordermap_csquare_le, THEN lt_trans1],
           (assumption | rule refl | erule ltI)+)
    apply (rule_tac i = "xa Un ya" and j = nat in Ord_linear2,
           simp_all add: Ord_Un Ord_nat)
    prefer 2 (*case nat le (xa Un ya) *)
     apply (simp add: le_imp_subset [THEN nat_succ_eqpoll, THEN cardinal_cong]
                      le_succ_iff InfCard_def Card_cardinal Un_least_lt Ord_Un
                    ltI nat_le_cardinal Ord_cardinal_le [THEN lt_trans1, THEN ltD])
    (*the finite case: xa Un ya < nat *)
    apply (rule_tac j = nat in lt_trans2)
     apply (simp add: lt_def nat_cmult_eq_mult nat_succI mult_type
                      nat_into_Card [THEN Card_cardinal_eq]  Ord_nat)
    apply (simp add: InfCard_def)
    done

    (*Main result: Kunen's Theorem 10.12*)
    lemma InfCard_csquare_eq: "InfCard(K) ==> K |*| K = K"
    apply (frule InfCard_is_Card [THEN Card_is_Ord])
    apply (erule rev_mp)
    apply (erule_tac i=K in trans_induct)
    apply (rule impI)
    apply (rule le_anti_sym)
    apply (erule_tac [2] InfCard_is_Card [THEN cmult_square_le])
    apply (rule ordertype_csquare_le [THEN [2] le_trans])
    apply (simp add: cmult_def Ord_cardinal_le
                     well_ord_csquare [THEN Ord_ordertype]
                     well_ord_csquare [THEN ordermap_bij, THEN bij_imp_eqpoll,
                                       THEN cardinal_cong], assumption+)
    done

    (*Corollary for arbitrary well-ordered sets (all sets, assuming AC)*)
    lemma well_ord_InfCard_square_eq:
         "[| well_ord(A,r);  InfCard(|A|) |] ==> A*A ≈ A"
    apply (rule prod_eqpoll_cong [THEN eqpoll_trans])
    apply (erule well_ord_cardinal_eqpoll [THEN eqpoll_sym])+
    apply (rule well_ord_cardinal_eqE)
    apply (blast intro: Ord_cardinal well_ord_rmult well_ord_Memrel, assumption)
    apply (simp add: cmult_def [symmetric] InfCard_csquare_eq)
    done

    lemma InfCard_square_eqpoll: "InfCard(K) ==> K × K ≈ K"
    apply (rule well_ord_InfCard_square_eq)
     apply (erule InfCard_is_Card [THEN Card_is_Ord, THEN well_ord_Memrel])
    apply (simp add: InfCard_is_Card [THEN Card_cardinal_eq])
    done

    lemma Inf_Card_is_InfCard: "[| ~Finite(i); Card(i) |] ==> InfCard(i)"
    by (simp add: InfCard_def Card_is_Ord [THEN nat_le_infinite_Ord])

    subsubsection{*Toward's Kunen's Corollary 10.13 (1)*}

    lemma InfCard_le_cmult_eq: "[| InfCard(K);  L le K;  0<L |] ==> K |*| L = K"
    apply (rule le_anti_sym)
     prefer 2
     apply (erule ltE, blast intro: cmult_le_self InfCard_is_Card)
    apply (frule InfCard_is_Card [THEN Card_is_Ord, THEN le_refl])
    apply (rule cmult_le_mono [THEN le_trans], assumption+)
    apply (simp add: InfCard_csquare_eq)
    done

    (*Corollary 10.13 (1), for cardinal multiplication*)
    lemma InfCard_cmult_eq: "[| InfCard(K);  InfCard(L) |] ==> K |*| L = K Un L"
    apply (rule_tac i = K and j = L in Ord_linear_le)
    apply (typecheck add: InfCard_is_Card Card_is_Ord)
    apply (rule cmult_commute [THEN ssubst])
    apply (rule Un_commute [THEN ssubst])
    apply (simp_all add: InfCard_is_Limit [THEN Limit_has_0] InfCard_le_cmult_eq
                         subset_Un_iff2 [THEN iffD1] le_imp_subset)
    done

    lemma InfCard_cdouble_eq: "InfCard(K) ==> K |+| K = K"
    apply (simp add: cmult_2 [symmetric] InfCard_is_Card cmult_commute)
    apply (simp add: InfCard_le_cmult_eq InfCard_is_Limit Limit_has_0 Limit_has_succ)
    done

    (*Corollary 10.13 (1), for cardinal addition*)
    lemma InfCard_le_cadd_eq: "[| InfCard(K);  L le K |] ==> K |+| L = K"
    apply (rule le_anti_sym)
     prefer 2
     apply (erule ltE, blast intro: cadd_le_self InfCard_is_Card)
    apply (frule InfCard_is_Card [THEN Card_is_Ord, THEN le_refl])
    apply (rule cadd_le_mono [THEN le_trans], assumption+)
    apply (simp add: InfCard_cdouble_eq)
    done

    lemma InfCard_cadd_eq: "[| InfCard(K);  InfCard(L) |] ==> K |+| L = K Un L"
    apply (rule_tac i = K and j = L in Ord_linear_le)
    apply (typecheck add: InfCard_is_Card Card_is_Ord)
    apply (rule cadd_commute [THEN ssubst])
    apply (rule Un_commute [THEN ssubst])
    apply (simp_all add: InfCard_le_cadd_eq subset_Un_iff2 [THEN iffD1] le_imp_subset)
    done

    (*The other part, Corollary 10.13 (2), refers to the cardinality of the set
      of all n-tuples of elements of K.  A better version for the Isabelle theory
      might be  InfCard(K) ==> |list(K)| = K.
    *)

    subsection{*For Every Cardinal Number There Exists A Greater One}

    text{*This result is Kunen's Theorem 10.16, which would be trivial using AC*}

    lemma Ord_jump_cardinal: "Ord(jump_cardinal(K))"
    apply (unfold jump_cardinal_def)
    apply (rule Ord_is_Transset [THEN [2] OrdI])
     prefer 2 apply (blast intro!: Ord_ordertype)
    apply (unfold Transset_def)
    apply (safe del: subsetI)
    apply (simp add: ordertype_pred_unfold, safe)
    apply (rule UN_I)
    apply (rule_tac [2] ReplaceI)
       prefer 4 apply (blast intro: well_ord_subset elim!: predE)+
    done

    (*Allows selective unfolding.  Less work than deriving intro/elim rules*)
    lemma jump_cardinal_iff:
         "i : jump_cardinal(K) <->
          (EX r X. r <= K*K & X <= K & well_ord(X,r) & i = ordertype(X,r))"
    apply (unfold jump_cardinal_def)
    apply (blast del: subsetI)
    done

    (*The easy part of Theorem 10.16: jump_cardinal(K) exceeds K*)
    lemma K_lt_jump_cardinal: "Ord(K) ==> K < jump_cardinal(K)"
    apply (rule Ord_jump_cardinal [THEN [2] ltI])
    apply (rule jump_cardinal_iff [THEN iffD2])
    apply (rule_tac x="Memrel(K)" in exI)
    apply (rule_tac x=K in exI)
    apply (simp add: ordertype_Memrel well_ord_Memrel)
    apply (simp add: Memrel_def subset_iff)
    done

    (*The proof by contradiction: the bijection f yields a wellordering of X
      whose ordertype is jump_cardinal(K).  *)
    lemma Card_jump_cardinal_lemma:
         "[| well_ord(X,r);  r <= K * K;  X <= K;
             f : bij(ordertype(X,r), jump_cardinal(K)) |]
          ==> jump_cardinal(K) : jump_cardinal(K)"
    apply (subgoal_tac "f O ordermap (X,r) : bij (X, jump_cardinal (K))")
     prefer 2 apply (blast intro: comp_bij ordermap_bij)
    apply (rule jump_cardinal_iff [THEN iffD2])
    apply (intro exI conjI)
    apply (rule subset_trans [OF rvimage_type Sigma_mono], assumption+)
    apply (erule bij_is_inj [THEN well_ord_rvimage])
    apply (rule Ord_jump_cardinal [THEN well_ord_Memrel])
    apply (simp add: well_ord_Memrel [THEN [2] bij_ordertype_vimage]
                     ordertype_Memrel Ord_jump_cardinal)
    done

    (*The hard part of Theorem 10.16: jump_cardinal(K) is itself a cardinal*)
    lemma Card_jump_cardinal: "Card(jump_cardinal(K))"
    apply (rule Ord_jump_cardinal [THEN CardI])
    apply (unfold eqpoll_def)
    apply (safe dest!: ltD jump_cardinal_iff [THEN iffD1])
    apply (blast intro: Card_jump_cardinal_lemma [THEN mem_irrefl])
    done

    subsection{*Basic Properties of Successor Cardinals*}

    lemma csucc_basic: "Ord(K) ==> Card(csucc(K)) & K < csucc(K)"
    apply (unfold csucc_def)
    apply (rule LeastI)
    apply (blast intro: Card_jump_cardinal K_lt_jump_cardinal Ord_jump_cardinal)+
    done

    lemmas Card_csucc = csucc_basic [THEN conjunct1, standard]

    lemmas lt_csucc = csucc_basic [THEN conjunct2, standard]

    lemma Ord_0_lt_csucc: "Ord(K) ==> 0 < csucc(K)"
    by (blast intro: Ord_0_le lt_csucc lt_trans1)

    lemma csucc_le: "[| Card(L);  K<L |] ==> csucc(K) le L"
    apply (unfold csucc_def)
    apply (rule Least_le)
    apply (blast intro: Card_is_Ord)+
    done

    lemma lt_csucc_iff: "[| Ord(i); Card(K) |] ==> i < csucc(K) <-> |i| le K"
    apply (rule iffI)
    apply (rule_tac [2] Card_lt_imp_lt)
    apply (erule_tac [2] lt_trans1)
    apply (simp_all add: lt_csucc Card_csucc Card_is_Ord)
    apply (rule notI [THEN not_lt_imp_le])
    apply (rule Card_cardinal [THEN csucc_le, THEN lt_trans1, THEN lt_irrefl], assumption)
    apply (rule Ord_cardinal_le [THEN lt_trans1])
    apply (simp_all add: Ord_cardinal Card_is_Ord)
    done

    lemma Card_lt_csucc_iff:
         "[| Card(K'); Card(K) |] ==> K' < csucc(K) <-> K' le K"
    by (simp add: lt_csucc_iff Card_cardinal_eq Card_is_Ord)

    lemma InfCard_csucc: "InfCard(K) ==> InfCard(csucc(K))"
    by (simp add: InfCard_def Card_csucc Card_is_Ord
                  lt_csucc [THEN leI, THEN [2] le_trans])

    subsubsection{*Removing elements from a finite set decreases its cardinality*}

    lemma Fin_imp_not_cons_lepoll: "A: Fin(U) ==> x~:A --> ~ cons(x,A) \<lesssim> A"
    apply (erule Fin_induct)
    apply (simp add: lepoll_0_iff)
    apply (subgoal_tac "cons (x,cons (xa,y)) = cons (xa,cons (x,y))")
    apply simp
    apply (blast dest!: cons_lepoll_consD, blast)
    done

    lemma Finite_imp_cardinal_cons [simp]:
         "[| Finite(A);  a~:A |] ==> |cons(a,A)| = succ(|A|)"
    apply (unfold cardinal_def)
    apply (rule Least_equality)
    apply (fold cardinal_def)
    apply (simp add: succ_def)
    apply (blast intro: cons_eqpoll_cong well_ord_cardinal_eqpoll
                 elim!: mem_irrefl  dest!: Finite_imp_well_ord)
    apply (blast intro: Card_cardinal Card_is_Ord)
    apply (rule notI)
    apply (rule Finite_into_Fin [THEN Fin_imp_not_cons_lepoll, THEN mp, THEN notE],
           assumption, assumption)
    apply (erule eqpoll_sym [THEN eqpoll_imp_lepoll, THEN lepoll_trans])
    apply (erule le_imp_lepoll [THEN lepoll_trans])
    apply (blast intro: well_ord_cardinal_eqpoll [THEN eqpoll_imp_lepoll]
                 dest!: Finite_imp_well_ord)
    done

    lemma Finite_imp_succ_cardinal_Diff:
         "[| Finite(A);  a:A |] ==> succ(|A-{a}|) = |A|"
    apply (rule_tac b = A in cons_Diff [THEN subst], assumption)
    apply (simp add: Finite_imp_cardinal_cons Diff_subset [THEN subset_Finite])
    apply (simp add: cons_Diff)
    done

    lemma Finite_imp_cardinal_Diff: "[| Finite(A);  a:A |] ==> |A-{a}| < |A|"
    apply (rule succ_leE)
    apply (simp add: Finite_imp_succ_cardinal_Diff)
    done

    lemma Finite_cardinal_in_nat [simp]: "Finite(A) ==> |A| : nat"
    apply (erule Finite_induct)
    apply (auto simp add: cardinal_0 Finite_imp_cardinal_cons)
    done

    lemma card_Un_Int:
         "[|Finite(A); Finite(B)|] ==> |A| #+ |B| = |A Un B| #+ |A Int B|"
    apply (erule Finite_induct, simp)
    apply (simp add: Finite_Int cons_absorb Un_cons Int_cons_left)
    done

    lemma card_Un_disjoint:
         "[|Finite(A); Finite(B); A Int B = 0|] ==> |A Un B| = |A| #+ |B|"
    by (simp add: Finite_Un card_Un_Int)

    lemma card_partition [rule_format]:
         "Finite(C) ==>
            Finite (\<Union> C) -->
            (∀c∈C. |c| = k) -->
            (∀c1 ∈ C. ∀c2 ∈ C. c1 ≠ c2 --> c1 ∩ c2 = 0) -->
            k #* |C| = |\<Union> C|"
    apply (erule Finite_induct, auto)
    apply (subgoal_tac " x ∩ \<Union>B = 0")
    apply (auto simp add: card_Un_disjoint Finite_Union
           subset_Finite [of _ "\<Union> (cons(x,F))"])
    done

    subsubsection{*Theorems by Krzysztof Grabczewski, proofs by lcp*}

    lemmas nat_implies_well_ord = nat_into_Ord [THEN well_ord_Memrel, standard]

    lemma nat_sum_eqpoll_sum: "[| m:nat; n:nat |] ==> m + n ≈ m #+ n"
    apply (rule eqpoll_trans)
    apply (rule well_ord_radd [THEN well_ord_cardinal_eqpoll, THEN eqpoll_sym])
    apply (erule nat_implies_well_ord)+
    apply (simp add: nat_cadd_eq_add [symmetric] cadd_def eqpoll_refl)
    done

    lemma Ord_subset_natD [rule_format]: "Ord(i) ==> i <= nat --> i : nat | i=nat"
    apply (erule trans_induct3, auto)
    apply (blast dest!: nat_le_Limit [THEN le_imp_subset])
    done

    lemma Ord_nat_subset_into_Card: "[| Ord(i); i <= nat |] ==> Card(i)"
    by (blast dest: Ord_subset_natD intro: Card_nat nat_into_Card)

    lemma Finite_Diff_sing_eq_diff_1: "[| Finite(A); x:A |] ==> |A-{x}| = |A| #- 1"
    apply (rule succ_inject)
    apply (rule_tac b = "|A|" in trans)
     apply (simp add: Finite_imp_succ_cardinal_Diff)
    apply (subgoal_tac "1 \<lesssim> A")
     prefer 2 apply (blast intro: not_0_is_lepoll_1)
    apply (frule Finite_imp_well_ord, clarify)
    apply (drule well_ord_lepoll_imp_Card_le)
     apply (auto simp add: cardinal_1)
    apply (rule trans)
     apply (rule_tac [2] diff_succ)
      apply (auto simp add: Finite_cardinal_in_nat)
    done

    lemma cardinal_lt_imp_Diff_not_0 [rule_format]:
         "Finite(B) ==> ALL A. |B|<|A| --> A - B ~= 0"
    apply (erule Finite_induct, auto)
    apply (case_tac "Finite (A)")
     apply (subgoal_tac [2] "Finite (cons (x, B))")
      apply (drule_tac [2] B = "cons (x, B) " in Diff_Finite)
       apply (auto simp add: Finite_0 Finite_cons)
    apply (subgoal_tac "|B|<|A|")
     prefer 2 apply (blast intro: lt_trans Ord_cardinal)
    apply (case_tac "x:A")
     apply (subgoal_tac [2] "A - cons (x, B) = A - B")
      apply auto
    apply (subgoal_tac "|A| le |cons (x, B) |")
     prefer 2
     apply (blast dest: Finite_cons [THEN Finite_imp_well_ord]
                  intro: well_ord_lepoll_imp_Card_le subset_imp_lepoll)
    apply (auto simp add: Finite_imp_cardinal_cons)
    apply (auto dest!: Finite_cardinal_in_nat simp add: le_iff)
    apply (blast intro: lt_trans)
    done

    ML{*
    val InfCard_def = thm "InfCard_def"
    val cmult_def = thm "cmult_def"
    val cadd_def = thm "cadd_def"
    val jump_cardinal_def = thm "jump_cardinal_def"
    val csucc_def = thm "csucc_def"

    val sum_commute_eqpoll = thm "sum_commute_eqpoll";
    val cadd_commute = thm "cadd_commute";
    val sum_assoc_eqpoll = thm "sum_assoc_eqpoll";
    val well_ord_cadd_assoc = thm "well_ord_cadd_assoc";
    val sum_0_eqpoll = thm "sum_0_eqpoll";
    val cadd_0 = thm "cadd_0";
    val sum_lepoll_self = thm "sum_lepoll_self";
    val cadd_le_self = thm "cadd_le_self";
    val sum_lepoll_mono = thm "sum_lepoll_mono";
    val cadd_le_mono = thm "cadd_le_mono";
    val eq_imp_not_mem = thm "eq_imp_not_mem";
    val sum_succ_eqpoll = thm "sum_succ_eqpoll";
    val nat_cadd_eq_add = thm "nat_cadd_eq_add";
    val prod_commute_eqpoll = thm "prod_commute_eqpoll";
    val cmult_commute = thm "cmult_commute";
    val prod_assoc_eqpoll = thm "prod_assoc_eqpoll";
    val well_ord_cmult_assoc = thm "well_ord_cmult_assoc";
    val sum_prod_distrib_eqpoll = thm "sum_prod_distrib_eqpoll";
    val well_ord_cadd_cmult_distrib = thm "well_ord_cadd_cmult_distrib";
    val prod_0_eqpoll = thm "prod_0_eqpoll";
    val cmult_0 = thm "cmult_0";
    val prod_singleton_eqpoll = thm "prod_singleton_eqpoll";
    val cmult_1 = thm "cmult_1";
    val prod_lepoll_self = thm "prod_lepoll_self";
    val cmult_le_self = thm "cmult_le_self";
    val prod_lepoll_mono = thm "prod_lepoll_mono";
    val cmult_le_mono = thm "cmult_le_mono";
    val prod_succ_eqpoll = thm "prod_succ_eqpoll";
    val nat_cmult_eq_mult = thm "nat_cmult_eq_mult";
    val cmult_2 = thm "cmult_2";
    val sum_lepoll_prod = thm "sum_lepoll_prod";
    val lepoll_imp_sum_lepoll_prod = thm "lepoll_imp_sum_lepoll_prod";
    val nat_cons_lepoll = thm "nat_cons_lepoll";
    val nat_cons_eqpoll = thm "nat_cons_eqpoll";
    val nat_succ_eqpoll = thm "nat_succ_eqpoll";
    val InfCard_nat = thm "InfCard_nat";
    val InfCard_is_Card = thm "InfCard_is_Card";
    val InfCard_Un = thm "InfCard_Un";
    val InfCard_is_Limit = thm "InfCard_is_Limit";
    val ordermap_eqpoll_pred = thm "ordermap_eqpoll_pred";
    val ordermap_z_lt = thm "ordermap_z_lt";
    val InfCard_le_cmult_eq = thm "InfCard_le_cmult_eq";
    val InfCard_cmult_eq = thm "InfCard_cmult_eq";
    val InfCard_cdouble_eq = thm "InfCard_cdouble_eq";
    val InfCard_le_cadd_eq = thm "InfCard_le_cadd_eq";
    val InfCard_cadd_eq = thm "InfCard_cadd_eq";
    val Ord_jump_cardinal = thm "Ord_jump_cardinal";
    val jump_cardinal_iff = thm "jump_cardinal_iff";
    val K_lt_jump_cardinal = thm "K_lt_jump_cardinal";
    val Card_jump_cardinal = thm "Card_jump_cardinal";
    val csucc_basic = thm "csucc_basic";
    val Card_csucc = thm "Card_csucc";
    val lt_csucc = thm "lt_csucc";
    val Ord_0_lt_csucc = thm "Ord_0_lt_csucc";
    val csucc_le = thm "csucc_le";
    val lt_csucc_iff = thm "lt_csucc_iff";
    val Card_lt_csucc_iff = thm "Card_lt_csucc_iff";
    val InfCard_csucc = thm "InfCard_csucc";
    val Finite_into_Fin = thm "Finite_into_Fin";
    val Fin_into_Finite = thm "Fin_into_Finite";
    val Finite_Fin_iff = thm "Finite_Fin_iff";
    val Finite_Un = thm "Finite_Un";
    val Finite_Union = thm "Finite_Union";
    val Finite_induct = thm "Finite_induct";
    val Fin_imp_not_cons_lepoll = thm "Fin_imp_not_cons_lepoll";
    val Finite_imp_cardinal_cons = thm "Finite_imp_cardinal_cons";
    val Finite_imp_succ_cardinal_Diff = thm "Finite_imp_succ_cardinal_Diff";
    val Finite_imp_cardinal_Diff = thm "Finite_imp_cardinal_Diff";
    val nat_implies_well_ord = thm "nat_implies_well_ord";
    val nat_sum_eqpoll_sum = thm "nat_sum_eqpoll_sum";
    val Diff_sing_Finite = thm "Diff_sing_Finite";
    val Diff_Finite = thm "Diff_Finite";
    val Ord_subset_natD = thm "Ord_subset_natD";
    val Ord_nat_subset_into_Card = thm "Ord_nat_subset_into_Card";
    val Finite_cardinal_in_nat = thm "Finite_cardinal_in_nat";
    val Finite_Diff_sing_eq_diff_1 = thm "Finite_Diff_sing_eq_diff_1";
    val cardinal_lt_imp_Diff_not_0 = thm "cardinal_lt_imp_Diff_not_0";
    *}

    end

lemma Card_Union:

      ∀x∈A. Card(x) ==> Card(\<Union>A)

lemma Card_UN:

      (!!x. x ∈ A ==> Card(K(x))) ==> Card(\<Union>x∈A. K(x))

lemma Card_OUN:

      (!!x. x ∈ A ==> Card(K(x))) ==> Card(\<Union>x<A. K(x))

lemma n_lesspoll_nat:

      n ∈ nat ==> n lesspoll nat

lemma in_Card_imp_lesspoll:

      [| Card(K); b ∈ K |] ==> b lesspoll K

lemma lesspoll_lemma:

      [| ¬ A lesspoll B; C lesspoll B |] ==> A - C ≠ 0

### Cardinal addition

#### Cardinal addition is commutative

lemma sum_commute_eqpoll:

      A + B ≈ B + A

lemma cadd_commute:

      i |+| j = j |+| i

#### Cardinal addition is associative

lemma sum_assoc_eqpoll:

      (A + B) + C ≈ A + B + C

lemma well_ord_cadd_assoc:

      [| well_ord(i, ri); well_ord(j, rj); well_ord(k, rk) |]
      ==> i |+| j |+| k = i |+| (j |+| k)

#### 0 is the identity for addition

lemma sum_0_eqpoll:

      0 + A ≈ A

lemma cadd_0:

      Card(K) ==> 0 |+| K = K

#### Addition by another cardinal

lemma sum_lepoll_self:

      A lepoll A + B

lemma cadd_le_self:

      [| Card(K); Ord(L) |] ==> K ≤ K |+| L

#### Monotonicity of addition

lemma sum_lepoll_mono:

      [| A lepoll C; B lepoll D |] ==> A + B lepoll C + D

lemma cadd_le_mono:

      [| K' ≤ K; L' ≤ L |] ==> K' |+| L' ≤ K |+| L

#### Addition of finite cardinals is "ordinary" addition

lemma sum_succ_eqpoll:

      succ(A) + B ≈ succ(A + B)

lemma cadd_succ_lemma:

      [| Ord(m); Ord(n) |] ==> succ(m) |+| n = |succ(m |+| n)|

lemma nat_cadd_eq_add:

      [| m ∈ nat; n ∈ nat |] ==> m |+| n = m #+ n

### Cardinal multiplication

#### Cardinal multiplication is commutative

lemma prod_commute_eqpoll:

      A × B ≈ B × A

lemma cmult_commute:

      i |*| j = j |*| i

#### Cardinal multiplication is associative

lemma prod_assoc_eqpoll:

      (A × B) × C ≈ A × B × C

lemma well_ord_cmult_assoc:

      [| well_ord(i, ri); well_ord(j, rj); well_ord(k, rk) |]
      ==> i |*| j |*| k = i |*| (j |*| k)

#### Cardinal multiplication distributes over addition

lemma sum_prod_distrib_eqpoll:

      (A + B) × C ≈ A × C + B × C

lemma well_ord_cadd_cmult_distrib:

      [| well_ord(i, ri); well_ord(j, rj); well_ord(k, rk) |]
      ==> (i |+| j) |*| k = i |*| k |+| j |*| k

#### Multiplication by 0 yields 0

lemma prod_0_eqpoll:

      0 × A ≈ 0

lemma cmult_0:

      0 |*| i = 0

#### 1 is the identity for multiplication

lemma prod_singleton_eqpoll:

      {x} × A ≈ A

lemma cmult_1:

      Card(K) ==> 1 |*| K = K

### Some inequalities for multiplication

lemma prod_square_lepoll:

      A lepoll A × A

lemma cmult_square_le:

      Card(K) ==> K ≤ K |*| K

#### Multiplication by a non-zero cardinal

lemma prod_lepoll_self:

      b ∈ B ==> A lepoll A × B

lemma cmult_le_self:

      [| Card(K); Ord(L); 0 < L |] ==> K ≤ K |*| L

#### Monotonicity of multiplication

lemma prod_lepoll_mono:

      [| A lepoll C; B lepoll D |] ==> A × B lepoll C × D

lemma cmult_le_mono:

      [| K' ≤ K; L' ≤ L |] ==> K' |*| L' ≤ K |*| L

### Multiplication of finite cardinals is "ordinary" multiplication

lemma prod_succ_eqpoll:

      succ(A) × B ≈ B + A × B

lemma cmult_succ_lemma:

      [| Ord(m); Ord(n) |] ==> succ(m) |*| n = n |+| m |*| n

lemma nat_cmult_eq_mult:

      [| m ∈ nat; n ∈ nat |] ==> m |*| n = m #× n

lemma cmult_2:

      Card(n) ==> 2 |*| n = n |+| n

lemma sum_lepoll_prod:

      2 lepoll C ==> B + B lepoll C × B

lemma lepoll_imp_sum_lepoll_prod:

      [| A lepoll B; 2 lepoll A |] ==> A + B lepoll A × B

### Infinite Cardinals are Limit Ordinals

lemma nat_cons_lepoll:

      nat lepoll A ==> cons(u, A) lepoll A

lemma nat_cons_eqpoll:

      nat lepoll A ==> cons(u, A) ≈ A

lemma nat_succ_eqpoll:

      nat ⊆ A ==> succ(A) ≈ A

lemma InfCard_nat:

      InfCard(nat)

lemma InfCard_is_Card:

      InfCard(K) ==> Card(K)

lemma InfCard_Un:

      [| InfCard(K); Card(L) |] ==> InfCard(K ∪ L)

lemma InfCard_is_Limit:

      InfCard(K) ==> Limit(K)

lemma ordermap_eqpoll_pred:

      [| well_ord(A, r); x ∈ A |] ==> ordermap(A, r) ` x ≈ Order.pred(A, x, r)

#### Establishing the well-ordering

lemma csquare_lam_inj:

      Ord(K) ==> (λ⟨x,y⟩∈K × K. ⟨x ∪ y, x, y⟩) ∈ inj(K × K, K × K × K)

lemma well_ord_csquare:

      Ord(K) ==> well_ord(K × K, csquare_rel(K))

#### Characterising initial segments of the well-ordering

lemma csquareD:

      [| ⟨⟨x, y⟩, z, z⟩ ∈ csquare_rel(K); x < K; y < K; z < K |] ==> x ≤ z ∧ y ≤ z

lemma pred_csquare_subset:

      z < K ==> Order.pred(K × K, ⟨z, z⟩, csquare_rel(K)) ⊆ succ(z) × succ(z)

lemma csquare_ltI:

      [| x < z; y < z; z < K |] ==> ⟨⟨x, y⟩, z, z⟩ ∈ csquare_rel(K)

lemma csquare_or_eqI:

      [| x ≤ z; y ≤ z; z < K |] ==> ⟨⟨x, y⟩, z, z⟩ ∈ csquare_rel(K) ∨ x = z ∧ y = z

#### The cardinality of initial segments

lemma ordermap_z_lt:

      [| Limit(K); x < K; y < K; z = succ(x ∪ y) |]
      ==> ordermap(K × K, csquare_rel(K)) ` ⟨x, y⟩ <
          ordermap(K × K, csquare_rel(K)) ` ⟨z, z⟩

lemma ordermap_csquare_le:

      [| Limit(K); x < K; y < K; z = succ(x ∪ y) |]
      ==> |ordermap(K × K, csquare_rel(K)) ` ⟨x, y⟩| ≤ |succ(z)| |*| |succ(z)|

lemma ordertype_csquare_le:

      [| InfCard(K); ∀y∈K. InfCard(y) --> y |*| y = y |]
      ==> ordertype(K × K, csquare_rel(K)) ≤ K

lemma InfCard_csquare_eq:

      InfCard(K) ==> K |*| K = K

lemma well_ord_InfCard_square_eq:

      [| well_ord(A, r); InfCard(|A|) |] ==> A × A ≈ A

lemma InfCard_square_eqpoll:

      InfCard(K) ==> K × K ≈ K

lemma Inf_Card_is_InfCard:

      [| ¬ Finite(i); Card(i) |] ==> InfCard(i)

#### Toward's Kunen's Corollary 10.13 (1)

lemma InfCard_le_cmult_eq:

      [| InfCard(K); L ≤ K; 0 < L |] ==> K |*| L = K

lemma InfCard_cmult_eq:

      [| InfCard(K); InfCard(L) |] ==> K |*| L = K ∪ L

lemma InfCard_cdouble_eq:

      InfCard(K) ==> K |+| K = K

lemma InfCard_le_cadd_eq:

      [| InfCard(K); L ≤ K |] ==> K |+| L = K

lemma InfCard_cadd_eq:

      [| InfCard(K); InfCard(L) |] ==> K |+| L = K ∪ L

### For Every Cardinal Number There Exists A Greater One} text{*This result is Kunen's Theorem 10.16, which would be trivial using AC

lemma Ord_jump_cardinal:

      Ord(jump_cardinal(K))

lemma jump_cardinal_iff:

      i ∈ jump_cardinal(K) <->
      (∃r X. r ⊆ K × K ∧ X ⊆ K ∧ well_ord(X, r) ∧ i = ordertype(X, r))

lemma K_lt_jump_cardinal:

      Ord(K) ==> K < jump_cardinal(K)

lemma Card_jump_cardinal_lemma:

      [| well_ord(X, r); r ⊆ K × K; X ⊆ K;
         f ∈ bij(ordertype(X, r), jump_cardinal(K)) |]
      ==> jump_cardinal(K) ∈ jump_cardinal(K)

lemma Card_jump_cardinal:

      Card(jump_cardinal(K))

### Basic Properties of Successor Cardinals

lemma csucc_basic:

      Ord(K) ==> Card(csucc(K)) ∧ K < csucc(K)

lemmas Card_csucc:

      Ord(K) ==> Card(csucc(K))

lemmas Card_csucc:

      Ord(K) ==> Card(csucc(K))

lemmas lt_csucc:

      Ord(K) ==> K < csucc(K)

lemmas lt_csucc:

      Ord(K) ==> K < csucc(K)

lemma Ord_0_lt_csucc:

      Ord(K) ==> 0 < csucc(K)

lemma csucc_le:

      [| Card(L); K < L |] ==> csucc(K) ≤ L

lemma lt_csucc_iff:

      [| Ord(i); Card(K) |] ==> i < csucc(K) <-> |i| ≤ K

lemma Card_lt_csucc_iff:

      [| Card(K'); Card(K) |] ==> K' < csucc(K) <-> K' ≤ K

lemma InfCard_csucc:

      InfCard(K) ==> InfCard(csucc(K))

#### Removing elements from a finite set decreases its cardinality

lemma Fin_imp_not_cons_lepoll:

      A ∈ Fin(U) ==> x ∉ A --> ¬ cons(x, A) lepoll A

lemma Finite_imp_cardinal_cons:

      [| Finite(A); a ∉ A |] ==> |cons(a, A)| = succ(|A|)

lemma Finite_imp_succ_cardinal_Diff:

      [| Finite(A); a ∈ A |] ==> succ(|A - {a}|) = |A|

lemma Finite_imp_cardinal_Diff:

      [| Finite(A); a ∈ A |] ==> |A - {a}| < |A|

lemma Finite_cardinal_in_nat:

      Finite(A) ==> |A| ∈ nat

lemma card_Un_Int:

      [| Finite(A); Finite(B) |] ==> |A| #+ |B| = |A ∪ B| #+ |A ∩ B|

lemma card_Un_disjoint:

      [| Finite(A); Finite(B); A ∩ B = 0 |] ==> |A ∪ B| = |A| #+ |B|

lemma card_partition:

      [| Finite(C); Finite(\<Union>C); !!c. c ∈ C ==> |c| = k;
         !!c1 c2. [| c1 ∈ C; c2 ∈ C; c1 ≠ c2 |] ==> c1 ∩ c2 = 0 |]
      ==> k #× |C| = |\<Union>C|

#### Theorems by Krzysztof Grabczewski, proofs by lcp

lemmas nat_implies_well_ord:

      i ∈ nat ==> well_ord(i, Memrel(i))

lemmas nat_implies_well_ord:

      i ∈ nat ==> well_ord(i, Memrel(i))

lemma nat_sum_eqpoll_sum:

      [| m ∈ nat; n ∈ nat |] ==> m + n ≈ m #+ n

lemma Ord_subset_natD:

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

lemma Ord_nat_subset_into_Card:

      [| Ord(i); i ⊆ nat |] ==> Card(i)

lemma Finite_Diff_sing_eq_diff_1:

      [| Finite(A); x ∈ A |] ==> |A - {x}| = |A| #- 1

lemma cardinal_lt_imp_Diff_not_0:

      [| Finite(B); |B| < |A| |] ==> A - B ≠ 0