Mercurial > hg > Members > kono > Proof > ZF-in-agda
annotate LEMC.agda @ 277:d9d3654baee1
seperate choice from LEM
author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
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date | Sat, 09 May 2020 09:38:21 +0900 |
parents | ODC.agda@6f10c47e4e7a |
children | 197e0b3d39dc |
rev | line source |
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16 | 1 open import Level |
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2 open import Ordinals |
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3 open import logic |
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4 open import Relation.Nullary |
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5 module LEMC {n : Level } (O : Ordinals {n} ) (p∨¬p : ( p : Set (suc n)) → p ∨ ( ¬ p )) where |
3 | 6 |
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7 open import zf |
23 | 8 open import Data.Nat renaming ( zero to Zero ; suc to Suc ; ℕ to Nat ; _⊔_ to _n⊔_ ) |
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9 open import Relation.Binary.PropositionalEquality |
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10 open import Data.Nat.Properties |
6 | 11 open import Data.Empty |
12 open import Relation.Binary | |
13 open import Relation.Binary.Core | |
14 | |
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15 open import nat |
276 | 16 import OD |
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17 |
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18 open inOrdinal O |
276 | 19 open OD O |
20 open OD.OD | |
21 open OD._==_ | |
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22 open ODAxiom odAxiom |
119 | 23 |
276 | 24 open import zfc |
190 | 25 |
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26 --- With assuption of OD is ordered, p ∨ ( ¬ p ) <=> axiom of choice |
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27 --- |
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28 record choiced ( X : OD) : Set (suc n) where |
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29 field |
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30 a-choice : OD |
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31 is-in : X ∋ a-choice |
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32 |
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33 open choiced |
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34 |
276 | 35 OD→ZFC : ZFC |
36 OD→ZFC = record { | |
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37 ZFSet = OD |
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38 ; _∋_ = _∋_ |
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39 ; _≈_ = _==_ |
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40 ; ∅ = od∅ |
28 | 41 ; Select = Select |
276 | 42 ; isZFC = isZFC |
28 | 43 } where |
276 | 44 -- infixr 200 _∈_ |
96 | 45 -- infixr 230 _∩_ _∪_ |
276 | 46 isZFC : IsZFC (OD ) _∋_ _==_ od∅ Select |
47 isZFC = record { | |
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48 choice-func = λ A {X} not A∋X → a-choice (choice-func X not ); |
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49 choice = λ A {X} A∋X not → is-in (choice-func X not) |
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50 } where |
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51 choice-func : (X : OD ) → ¬ ( X == od∅ ) → choiced X |
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52 choice-func X not = have_to_find where |
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53 ψ : ( ox : Ordinal ) → Set (suc n) |
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54 ψ ox = (( x : Ordinal ) → x o< ox → ( ¬ def X x )) ∨ choiced X |
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55 lemma-ord : ( ox : Ordinal ) → ψ ox |
235 | 56 lemma-ord ox = TransFinite {ψ} induction ox where |
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57 ∋-p : (A x : OD ) → Dec ( A ∋ x ) |
271 | 58 ∋-p A x with p∨¬p (Lift (suc n) ( A ∋ x )) -- LEM |
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59 ∋-p A x | case1 (lift t) = yes t |
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60 ∋-p A x | case2 t = no (λ x → t (lift x )) |
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61 ∀-imply-or : {A : Ordinal → Set n } {B : Set (suc n) } |
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62 → ((x : Ordinal ) → A x ∨ B) → ((x : Ordinal ) → A x) ∨ B |
271 | 63 ∀-imply-or {A} {B} ∀AB with p∨¬p (Lift ( suc n ) ((x : Ordinal ) → A x)) -- LEM |
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64 ∀-imply-or {A} {B} ∀AB | case1 (lift t) = case1 t |
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65 ∀-imply-or {A} {B} ∀AB | case2 x = case2 (lemma (λ not → x (lift not ))) where |
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66 lemma : ¬ ((x : Ordinal ) → A x) → B |
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67 lemma not with p∨¬p B |
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68 lemma not | case1 b = b |
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69 lemma not | case2 ¬b = ⊥-elim (not (λ x → dont-orb (∀AB x) ¬b )) |
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70 induction : (x : Ordinal) → ((y : Ordinal) → y o< x → ψ y) → ψ x |
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71 induction x prev with ∋-p X ( ord→od x) |
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72 ... | yes p = case2 ( record { a-choice = ord→od x ; is-in = p } ) |
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73 ... | no ¬p = lemma where |
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74 lemma1 : (y : Ordinal) → (y o< x → def X y → ⊥) ∨ choiced X |
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75 lemma1 y with ∋-p X (ord→od y) |
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76 lemma1 y | yes y<X = case2 ( record { a-choice = ord→od y ; is-in = y<X } ) |
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77 lemma1 y | no ¬y<X = case1 ( λ lt y<X → ¬y<X (subst (λ k → def X k ) (sym diso) y<X ) ) |
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78 lemma : ((y : Ordinals.ord O) → (O Ordinals.o< y) x → def X y → ⊥) ∨ choiced X |
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79 lemma = ∀-imply-or lemma1 |
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80 have_to_find : choiced X |
271 | 81 have_to_find = dont-or (lemma-ord (od→ord X )) ¬¬X∋x where |
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82 ¬¬X∋x : ¬ ((x : Ordinal) → x o< (od→ord X) → def X x → ⊥) |
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83 ¬¬X∋x nn = not record { |
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84 eq→ = λ {x} lt → ⊥-elim (nn x (def→o< lt) lt) |
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85 ; eq← = λ {x} lt → ⊥-elim ( ¬x<0 lt ) |
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86 } |
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87 |