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Third definition added
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cesarbm03 committed Oct 3, 2023
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18 changes: 16 additions & 2 deletions src/simplicial-hott/13-limits.rzk.md
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Expand Up @@ -93,7 +93,6 @@ Another definition of limit.
( A B : U)
( is-segal-B : is-segal B)
( f : A → B)
( is-segal-B : is-segal B)
: U
:= Σ (b : B),
Σ ( c : cone2 A B f b ),
Expand Down Expand Up @@ -136,14 +135,29 @@ Another definition of colimit.
( A B : U)
( is-segal-B : is-segal B)
( f : A → B)
( is-segal-B : is-segal B)
: U
:= Σ (b : B),
Σ ( c : cocone2 A B f b ),
( x : B) → ( k : hom B x b)
→ is-equiv (cocone2 A B f x) (cocone2 A B f b) (cocone-postcomposition A B is-segal-B f x b k )
```
The following alternative definition does not require a Segalness condition. When
`#!rzk is-segal B` then definitions 1 and 3 coincide.

```rzk
#def limit3
( A B : U)
( f : A → B)
: U
:= Σ ( b : B),(x : B) → Equiv (hom B b x ) (cone2 A B f x)
```
```rzk
#def colimit3
( A B : U)
( f : A → B)
: U
:= Σ ( b : B),(x : B) → Equiv (hom B x b ) (cocone2 A B f x)
```

## Uniqueness of initial and final objects.

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