# Theory Hartog

theory Hartog
imports AC_Equiv
```(*  Title:      ZF/AC/Hartog.thy
Author:     Krzysztof Grabczewski

Hartog's function.
*)

theory Hartog
imports AC_Equiv
begin

definition
Hartog :: "i => i"  where
"Hartog(X) == μ i. ~ i ≲ X"

lemma Ords_in_set: "∀a. Ord(a) ⟶ a ∈ X ==> P"
apply (rule_tac X = "{y ∈ X. Ord (y) }" in ON_class [elim_format])
apply fast
done

lemma Ord_lepoll_imp_ex_well_ord:
"[| Ord(a); a ≲ X |]
==> ∃Y. Y ⊆ X & (∃R. well_ord(Y,R) & ordertype(Y,R)=a)"
apply (unfold lepoll_def)
apply (erule exE)
apply (intro exI conjI)
apply (erule inj_is_fun [THEN fun_is_rel, THEN image_subset])
apply (rule well_ord_rvimage [OF bij_is_inj well_ord_Memrel])
apply (erule restrict_bij [THEN bij_converse_bij])
apply (rule subset_refl, assumption)
apply (rule trans)
apply (rule bij_ordertype_vimage)
apply (erule restrict_bij [THEN bij_converse_bij])
apply (rule subset_refl)
apply (erule well_ord_Memrel)
apply (erule ordertype_Memrel)
done

lemma Ord_lepoll_imp_eq_ordertype:
"[| Ord(a); a ≲ X |] ==> ∃Y. Y ⊆ X & (∃R. R ⊆ X*X & ordertype(Y,R)=a)"
apply (drule Ord_lepoll_imp_ex_well_ord, assumption, clarify)
apply (intro exI conjI)
apply (erule_tac [3] ordertype_Int, auto)
done

lemma Ords_lepoll_set_lemma:
"(∀a. Ord(a) ⟶ a ≲ X) ==>
∀a. Ord(a) ⟶
a ∈ {b. Z ∈ Pow(X)*Pow(X*X), ∃Y R. Z=<Y,R> & ordertype(Y,R)=b}"
apply (intro allI impI)
apply (elim allE impE, assumption)
apply (blast dest!: Ord_lepoll_imp_eq_ordertype intro: sym)
done

lemma Ords_lepoll_set: "∀a. Ord(a) ⟶ a ≲ X ==> P"
by (erule Ords_lepoll_set_lemma [THEN Ords_in_set])

lemma ex_Ord_not_lepoll: "∃a. Ord(a) & ~a ≲ X"
apply (rule ccontr)
apply (best intro: Ords_lepoll_set)
done

lemma not_Hartog_lepoll_self: "~ Hartog(A) ≲ A"
apply (unfold Hartog_def)
apply (rule ex_Ord_not_lepoll [THEN exE])
apply (rule LeastI, auto)
done

lemmas Hartog_lepoll_selfE = not_Hartog_lepoll_self [THEN notE]

lemma Ord_Hartog: "Ord(Hartog(A))"
by (unfold Hartog_def, rule Ord_Least)

lemma less_HartogE1: "[| i < Hartog(A); ~ i ≲ A |] ==> P"
by (unfold Hartog_def, fast elim: less_LeastE)

lemma less_HartogE: "[| i < Hartog(A); i ≈ Hartog(A) |] ==> P"
by (blast intro: less_HartogE1 eqpoll_sym eqpoll_imp_lepoll
lepoll_trans [THEN Hartog_lepoll_selfE])

lemma Card_Hartog: "Card(Hartog(A))"
by (fast intro!: CardI Ord_Hartog elim: less_HartogE)

end
```