Library kuratowski.kuratowski_sets
Definitions of the Kuratowski-finite sets via a HIT.
We do not need the computation rules in the development, so they are not present here.
Require Import HoTT HitTactics.
Require Export set_names lattice_examples.
Module Export FSet.
Section FSet.
Private Inductive FSet (A : Type) : Type :=
| E : FSet A
| L : A → FSet A
| U : FSet A → FSet A → FSet A.
Global Instance fset_empty : ∀ A, hasEmpty (FSet A) := E.
Global Instance fset_singleton : ∀ A, hasSingleton (FSet A) A := L.
Global Instance fset_union : ∀ A, hasUnion (FSet A) := U.
Variable A : Type.
Axiom assoc : ∀ (x y z : FSet A),
x ∪ (y ∪ z) = (x ∪ y) ∪ z.
Axiom comm : ∀ (x y : FSet A),
x ∪ y = y ∪ x.
Axiom nl : ∀ (x : FSet A),
∅ ∪ x = x.
Axiom nr : ∀ (x : FSet A),
x ∪ ∅ = x.
Axiom idem : ∀ (x : A),
{|x|} ∪ {|x|} = {|x|}.
Axiom trunc : IsHSet (FSet A).
End FSet.
Arguments assoc {_} _ _ _.
Arguments comm {_} _ _.
Arguments nl {_} _.
Arguments nr {_} _.
Arguments idem {_} _.
Section FSet_induction.
Variable (A : Type)
(P : FSet A → Type)
(H : ∀ X : FSet A, IsHSet (P X))
(eP : P ∅)
(lP : ∀ a: A, P {|a|})
(uP : ∀ (x y: FSet A), P x → P y → P (x ∪ y))
(assocP : ∀ (x y z : FSet A)
(px: P x) (py: P y) (pz: P z),
assoc x y z #
(uP x (y ∪ z) px (uP y z py pz))
=
(uP (x ∪ y) z (uP x y px py) pz))
(commP : ∀ (x y: FSet A) (px: P x) (py: P y),
comm x y #
uP x y px py = uP y x py px)
(nlP : ∀ (x : FSet A) (px: P x),
nl x # uP ∅ x eP px = px)
(nrP : ∀ (x : FSet A) (px: P x),
nr x # uP x ∅ px eP = px)
(idemP : ∀ (x : A),
idem x # uP {|x|} {|x|} (lP x) (lP x) = lP x).
Fixpoint FSet_ind
(x : FSet A)
{struct x}
: P x
:= (match x return _ → _ → _ → _ → _ → _ → P x with
| E ⇒ fun _ _ _ _ _ _ ⇒ eP
| L a ⇒ fun _ _ _ _ _ _ ⇒ lP a
| U y z ⇒ fun _ _ _ _ _ _ ⇒ uP y z (FSet_ind y) (FSet_ind z)
end) H assocP commP nlP nrP idemP.
End FSet_induction.
Section FSet_recursion.
Variable (A : Type)
(P : Type)
(H: IsHSet P)
(e : P)
(l : A → P)
(u : P → P → P)
(assocP : ∀ (x y z : P), u x (u y z) = u (u x y) z)
(commP : ∀ (x y : P), u x y = u y x)
(nlP : ∀ (x : P), u e x = x)
(nrP : ∀ (x : P), u x e = x)
(idemP : ∀ (x : A), u (l x) (l x) = l x).
Definition FSet_rec : FSet A → P.
Proof.
simple refine (FSet_ind A _ _ _ _ _ _ _ _ _ _)
; try (intros ; simple refine ((transport_const _ _) @ _)) ; cbn.
- apply e.
- apply l.
- intros x y ; apply u.
- apply assocP.
- apply commP.
- apply nlP.
- apply nrP.
- apply idemP.
Defined.
End FSet_recursion.
Instance FSet_recursion A : HitRecursion (FSet A) :=
{
indTy := _; recTy := _;
H_inductor := FSet_ind A; H_recursor := FSet_rec A
}.
End FSet.
Lemma union_idem {A : Type} : ∀ x: FSet A, x ∪ x = x.
Proof.
hinduction ; try (intros ; apply set_path2).
- apply nl.
- apply idem.
- intros x y P Q.
rewrite assoc.
rewrite (comm x y).
rewrite <- (assoc y x x).
rewrite P.
rewrite (comm y x).
rewrite <- (assoc x y y).
apply (ap (x ∪) Q).
Defined.
Section relations.
Context `{Univalence}.
Require Export set_names lattice_examples.
Module Export FSet.
Section FSet.
Private Inductive FSet (A : Type) : Type :=
| E : FSet A
| L : A → FSet A
| U : FSet A → FSet A → FSet A.
Global Instance fset_empty : ∀ A, hasEmpty (FSet A) := E.
Global Instance fset_singleton : ∀ A, hasSingleton (FSet A) A := L.
Global Instance fset_union : ∀ A, hasUnion (FSet A) := U.
Variable A : Type.
Axiom assoc : ∀ (x y z : FSet A),
x ∪ (y ∪ z) = (x ∪ y) ∪ z.
Axiom comm : ∀ (x y : FSet A),
x ∪ y = y ∪ x.
Axiom nl : ∀ (x : FSet A),
∅ ∪ x = x.
Axiom nr : ∀ (x : FSet A),
x ∪ ∅ = x.
Axiom idem : ∀ (x : A),
{|x|} ∪ {|x|} = {|x|}.
Axiom trunc : IsHSet (FSet A).
End FSet.
Arguments assoc {_} _ _ _.
Arguments comm {_} _ _.
Arguments nl {_} _.
Arguments nr {_} _.
Arguments idem {_} _.
Section FSet_induction.
Variable (A : Type)
(P : FSet A → Type)
(H : ∀ X : FSet A, IsHSet (P X))
(eP : P ∅)
(lP : ∀ a: A, P {|a|})
(uP : ∀ (x y: FSet A), P x → P y → P (x ∪ y))
(assocP : ∀ (x y z : FSet A)
(px: P x) (py: P y) (pz: P z),
assoc x y z #
(uP x (y ∪ z) px (uP y z py pz))
=
(uP (x ∪ y) z (uP x y px py) pz))
(commP : ∀ (x y: FSet A) (px: P x) (py: P y),
comm x y #
uP x y px py = uP y x py px)
(nlP : ∀ (x : FSet A) (px: P x),
nl x # uP ∅ x eP px = px)
(nrP : ∀ (x : FSet A) (px: P x),
nr x # uP x ∅ px eP = px)
(idemP : ∀ (x : A),
idem x # uP {|x|} {|x|} (lP x) (lP x) = lP x).
Fixpoint FSet_ind
(x : FSet A)
{struct x}
: P x
:= (match x return _ → _ → _ → _ → _ → _ → P x with
| E ⇒ fun _ _ _ _ _ _ ⇒ eP
| L a ⇒ fun _ _ _ _ _ _ ⇒ lP a
| U y z ⇒ fun _ _ _ _ _ _ ⇒ uP y z (FSet_ind y) (FSet_ind z)
end) H assocP commP nlP nrP idemP.
End FSet_induction.
Section FSet_recursion.
Variable (A : Type)
(P : Type)
(H: IsHSet P)
(e : P)
(l : A → P)
(u : P → P → P)
(assocP : ∀ (x y z : P), u x (u y z) = u (u x y) z)
(commP : ∀ (x y : P), u x y = u y x)
(nlP : ∀ (x : P), u e x = x)
(nrP : ∀ (x : P), u x e = x)
(idemP : ∀ (x : A), u (l x) (l x) = l x).
Definition FSet_rec : FSet A → P.
Proof.
simple refine (FSet_ind A _ _ _ _ _ _ _ _ _ _)
; try (intros ; simple refine ((transport_const _ _) @ _)) ; cbn.
- apply e.
- apply l.
- intros x y ; apply u.
- apply assocP.
- apply commP.
- apply nlP.
- apply nrP.
- apply idemP.
Defined.
End FSet_recursion.
Instance FSet_recursion A : HitRecursion (FSet A) :=
{
indTy := _; recTy := _;
H_inductor := FSet_ind A; H_recursor := FSet_rec A
}.
End FSet.
Lemma union_idem {A : Type} : ∀ x: FSet A, x ∪ x = x.
Proof.
hinduction ; try (intros ; apply set_path2).
- apply nl.
- apply idem.
- intros x y P Q.
rewrite assoc.
rewrite (comm x y).
rewrite <- (assoc y x x).
rewrite P.
rewrite (comm y x).
rewrite <- (assoc x y y).
apply (ap (x ∪) Q).
Defined.
Section relations.
Context `{Univalence}.
Membership of finite sets.
Global Instance fset_member : ∀ A, hasMembership (FSet A) A.
Proof.
intros A a.
hrecursion.
- apply False_hp.
- apply (fun a' ⇒ merely(a = a')).
- apply lor.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
Defined.
Proof.
intros A a.
hrecursion.
- apply False_hp.
- apply (fun a' ⇒ merely(a = a')).
- apply lor.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
Defined.
Subset relation of finite sets.
Global Instance fset_subset : ∀ A, hasSubset (FSet A).
Proof.
intros A X Y.
hrecursion X.
- apply Unit_hp.
- apply (fun a ⇒ a ∈ Y).
- intros X1 X2.
∃ (prod X1 X2).
exact _.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- intros.
apply path_trunctype ; apply prod_unit_l.
- intros.
apply path_trunctype ; apply prod_unit_r.
- eauto with lattice_hints typeclass_instances.
Defined.
End relations.
Proof.
intros A X Y.
hrecursion X.
- apply Unit_hp.
- apply (fun a ⇒ a ∈ Y).
- intros X1 X2.
∃ (prod X1 X2).
exact _.
- eauto with lattice_hints typeclass_instances.
- eauto with lattice_hints typeclass_instances.
- intros.
apply path_trunctype ; apply prod_unit_l.
- intros.
apply path_trunctype ; apply prod_unit_r.
- eauto with lattice_hints typeclass_instances.
Defined.
End relations.