From: Favonia <favonia@gmail.com>
To: "Martín Hötzel Escardó" <escardo.martin@gmail.com>
Cc: Homotopy Type Theory <HomotopyTypeTheory@googlegroups.com>
Subject: Re: [HoTT] Re: Agda formalization question
Date: Tue, 26 Jun 2018 15:15:52 -0400 [thread overview]
Message-ID: <CAN2iy-SrB4asBz8xiMv8iJEyipnhRZSi1L7JrULD8a574PGbgw@mail.gmail.com> (raw)
In-Reply-To: <b006dce7-d31e-42b6-ae44-de19652e8087@googlegroups.com>
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Hi Martin,
I don't know your definition of is-prop, but how about this?
open import Agda.Primitive
_* : ∀ U → Set (lsuc U)
U * = Set U
data _≡_ {U} {X : U *} (x : X) : X → U * where
refl : x ≡ x
is-prop : ∀ {U} → U * → U *
is-prop X = (x y : X) → x ≡ y
is-set : ∀ {U} → U * → U *
is-set X = {x y : X} → is-prop (x ≡ y)
is-set' : ∀ {U} → U * → U *
is-set' X = (x y : X) → is-prop (x ≡ y)
is-set'-is-set : ∀ {U} {X : U *} → is-set' X → is-set X
is-set'-is-set s {x} {y} = s x y
is-set-is-set' : ∀ {U} {X : U *} → is-set X → is-set' X
is-set-is-set' s x y = s {x} {y}
funext : ∀ U0 U1 → lsuc (U0 ⊔ U1) *
funext U0 U1 = {X : U0 *} {Y : X → U1 *} (f g : (x : X) → Y x) → (∀ x → f x
≡ g x) → f ≡ g
postulate
is-prop-is-set' : ∀ {U} {X : U *} → funext U U → is-prop (is-set' X)
ap : ∀ {U0 U1} {X : U0 *} {Y : U1 *} (f : X → Y) {x y : X} → x ≡ y → f x ≡
f y
ap f refl = refl
is-prop-is-set : ∀ {U} {X : U *} → funext U U → is-prop (is-set X)
is-prop-is-set fe isset0 isset1 =
ap is-set'-is-set (is-prop-is-set' fe (is-set-is-set' isset0)
(is-set-is-set' isset1))
Best,
Favonia
On Wed, Jun 20, 2018 at 3:46 PM Martín Hötzel Escardó <
escardo.martin@gmail.com> wrote:
> Bad copy and paste. Let me fix this.
>
>
> is-set : ∀ {U} → U ̇ → U ̇
> is-set X = {x y : X} → is-prop(x ≡ y)
>
> is-set' : ∀ {U} → U ̇ → U ̇
> is-set' X = (x y : X) → is-prop(x ≡ y)
>
> Martin
>
>>
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next prev parent reply other threads:[~2018-06-26 19:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 19:43 [HoTT] " Martín Hötzel Escardó
2018-06-20 19:46 ` [HoTT] " Martín Hötzel Escardó
2018-06-26 19:15 ` Favonia [this message]
2018-06-26 20:00 ` Martín Hötzel Escardó
2018-06-26 20:42 ` Favonia
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