notation "hvbox(a break ◃ b)" non associative with precedence 45
for @{ 'covers $a $b }.
-interpretation "covers" 'covers a U = (covers _ U a).
interpretation "coversl" 'covers A U = (coversl _ U A).
+interpretation "covers" 'covers a U = (covers _ U a).
definition covers_elim ≝
λA:axiom_set.λU: 2 \sup A.λP:2 \sup A.
coinductive fish (A:axiom_set) (U: 2 \sup A) : A → CProp ≝
mk_fish: ∀a:A. (a ∈ U ∧ ∀j: i ? a. ∃y: A. y ∈ C ? a j ∧ fish A U y) → fish A U a.
+definition fishl ≝ λA:axiom_set.λU:2 \sup A.λV:2 \sup A. ∃a. a ∈ V ∧ fish ? U a.
notation "hvbox(a break ⋉ b)" non associative with precedence 45
for @{ 'fish $a $b }.
+interpretation "fishl" 'fish A U = (fishl _ U A).
interpretation "fish" 'fish a U = (fish _ U a).
let corec fish_rec (A:axiom_set) (U: 2 \sup A)
theorem transitivity: ∀A:axiom_set.∀a:A.∀U,V. a ◃ U → U ◃ V → a ◃ V.
intros;
- apply (covers_elim ?? (mk_powerset A (λa.a ◃ V)) ??? H); intros;
+ apply (covers_elim ?? (mk_powerset A (λa.a ◃ V)) ??? H); simplify; intros;
[ cases H1 in H2;
intro;
apply H2;
qed.
theorem cotransitivity:
- ∀A:axiom_set.∀a:A.∀U,V. a ⋉ U → (∀b. b ⋉ U → b ∈ V) → a ⋉ V.
+ ∀A:axiom_set.∀a:A.∀U,V. a ⋉ U → (∀b:A. b ⋉ U → b ∈ V) → a ⋉ V.
intros;
apply (fish_rec ?? (mk_powerset A (λa.a ⋉ U)) ??? H); simplify; intros;
[ apply H1;
assumption
| cases H2 in j; clear H2; cases H3; clear H3;
assumption]
+qed.
+
+theorem compatibility: ∀A:axiom_set.∀a:A.∀U,V. a ⋉ V → a ◃ U → U ⋉ V.
+ intros;
+ generalize in match H; clear H; generalize in match V; clear V;
+ apply (covers_elim ?? (mk_powerset A (λa.∀p:2 \sup A.a ⋉ p → U ⋉ p)) ??? H1);
+ clear H1; simplify; intros;
+ [ exists [apply a1]
+ split;
+ assumption
+ | cases H2 in j H H1; clear H2 a1; intros;
+ cases H; clear H;
+ cases (H4 i); clear H4; cases H; clear H;
+ apply (H2 w); clear H2;
+ assumption]
qed.
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