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chore: fix separators
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TOTBWF committed Aug 12, 2024
1 parent 40a0b88 commit 6d6ca43
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2 changes: 1 addition & 1 deletion src/Cat/Diagram/Coequaliser/RegularEpi.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,7 @@ follows by yet more brute-force calculation.
(∐F.universal _ _ C.∘ ∐Ob.match F.₀ ∐F.ψ) C.∘ ∐Ob.ι F.₀ j ≡⟨ C.pullr (∐Ob.commute _) ⟩
∐F.universal _ _ C.∘ ∐F.ψ j ≡⟨ ∐F.factors _ _ ⟩
e' C.∘ ∐Ob.ι F.₀ j ∎
indexed-coproduct→regular-epi .has-is-coeq .unique {e' = e'} {colim = h} p =
indexed-coproduct→regular-epi .has-is-coeq .unique {e' = e'} {other = h} p =
∐F.unique _ _ _ λ j
h C.∘ ∐F.ψ j ≡˘⟨ ap₂ C._∘_ refl (∐Ob.commute _) ⟩
h C.∘ (∐Ob.match F.₀ ∐F.ψ C.∘ ∐Ob.ι F.₀ j) ≡⟨ C.pulll p ⟩
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28 changes: 14 additions & 14 deletions src/Cat/Diagram/Separator.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -264,7 +264,7 @@ $S$ is a separating family.
```agda
equalisers+conservative→separator
: {s}
has-equalisers C
Equalisers C
is-conservative (Hom-from C s)
is-separator s
```
Expand All @@ -276,24 +276,24 @@ $e$ being an equaliser.

```agda
equalisers+conservative→separator equalisers f∘-conservative {f = f} {g = g} p =
invertible→epic equ-invertible f g Eq.equal
invertible→epic equ-invertible f g equal
where
module Eq = Equaliser (equalisers f g)
open Equalisers equalisers
```

Moreover, $\cC(S,-)$ is conservative, so it suffices to prove that
precomposition of $e$ with an $S$-generalized element is an equivalence.
This follows immediately from the universal property of equalisers!

```agda
equ-invertible : is-invertible Eq.equ
equ-invertible : is-invertible (equ f g)
equ-invertible =
f∘-conservative $
is-equiv→is-invertible $
is-iso→is-equiv $ iso
(λ e Eq.universal (p e))
(λ e Eq.factors)
(λ h sym (Eq.unique refl))
(λ e equalise e (p e))
(λ e equ∘equalise)
(λ h sym (equalise-unique refl))
```

A similar line of argument lets us generalize this result to separating
Expand All @@ -302,7 +302,7 @@ families.
```agda
equalisers+jointly-conservative→separating-family
: {κ} {Idx : Type κ} {sᵢ : Idx Ob}
has-equalisers C
Equalisers C
is-jointly-conservative (λ i Hom-from C (sᵢ i))
is-separating-family sᵢ
```
Expand All @@ -313,18 +313,18 @@ equalisers+jointly-conservative→separating-family
```agda
equalisers+jointly-conservative→separating-family
equalisers fᵢ∘-conservative {f = f} {g = g} p =
invertible→epic equ-invertible f g Eq.equal
invertible→epic equ-invertible f g equal
where
module Eq = Equaliser (equalisers f g)
open Equalisers equalisers

equ-invertible : is-invertible Eq.equ
equ-invertible : is-invertible (equ f g)
equ-invertible =
fᵢ∘-conservative λ i
is-equiv→is-invertible $
is-iso→is-equiv $ iso
(λ eᵢ Eq.universal (p eᵢ))
(λ eᵢ Eq.factors)
(λ h sym (Eq.unique refl))
(λ eᵢ equalise eᵢ (p eᵢ))
(λ eᵢ equ∘equalise)
(λ h sym (equalise-unique refl))
```
</details>

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2 changes: 1 addition & 1 deletion src/Cat/Diagram/Separator/Regular.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -135,7 +135,7 @@ This is straightforward enough to prove with sufficient elbow grease.
(dense.universal _ ∘ ⊗!.match _ _ _) ∘ ⊗!.ι _ _ e ≡⟨ pullr (⊗!.commute _ _) ⟩
dense.universal _ ∘ e ≡⟨ dense.commute ⟩
e' ∘ ⊗!.ι _ _ e ∎
regular .has-is-coeq .unique {e' = e'} {colim = h} p =
regular .has-is-coeq .unique {e' = e'} {other = h} p =
dense.unique _ λ e
h ∘ e ≡˘⟨ ap (h ∘_) (⊗!.commute (Hom s x) s) ⟩
h ∘ ⊗!.match _ _ _ ∘ ⊗!.ι _ _ e ≡⟨ pulll p ⟩
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