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slightly better prose
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fredrik-bakke committed Feb 24, 2024
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17 changes: 8 additions & 9 deletions src/foundation-core/pullbacks.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -39,18 +39,17 @@ Given a [cospan of types](foundation.cospans.md)

we want to pose the question of whether a certain
[cone](foundation.cones-over-cospan-diagrams.md) over it is a
{{#concept "pullback cone" Disambiguation="types" Agda=is-pullback}}. This is
concept is captured by
{{#concept "pullback cone" Disambiguation="types" Agda=is-pullback}}. Although
this concept is captured by
[the universal property of the pullback](foundation-core.universal-property-pullbacks.md),
however, the universal property is a large proposition so it is not suitable for
all purposes.
this is a large proposition, which is not suitable for all purposes.

As an alternative, given the existence of the
Therefore, as our main definition of a pullback cone we consider
{{#concept "the small predicate of being a pullback" Agda=is-pullback}}: given
the existence of the
[standard pullback type](foundation-core.standard-pullbacks.md) `A ×_X B`, we
can characterize pullback cones as those for which the gap map from the standard
pullback is an [equivalence](foundation-core.equivalences.md). This predicate is
a small [proposition](foundation-core.propositions.md) that we dub
{{#concept "the small predicate of being a pullback" Agda=is-pullback}}.
can characterize pullback cones as those for which the gap map into the standard
pullback is an [equivalence](foundation-core.equivalences.md).

## Definitions

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17 changes: 8 additions & 9 deletions src/foundation/pullbacks.lagda.md
Original file line number Diff line number Diff line change
Expand Up @@ -53,18 +53,17 @@ Given a [cospan of types](foundation.cospans.md)

we want to pose the question of whether a certain
[cone](foundation.cones-over-cospan-diagrams.md) over it is a
{{#concept "pullback cone" Disambiguation="types" Agda=is-pullback}}. This is
concept is captured by
{{#concept "pullback cone" Disambiguation="types" Agda=is-pullback}}. Although
this concept is captured by
[the universal property of the pullback](foundation-core.universal-property-pullbacks.md),
however, the universal property is a large proposition so it is not suitable for
all purposes.
this is a large proposition, which is not suitable for all purposes.

As an alternative, given the existence of the
Therefore, as our main definition of a pullback cone we consider
{{#concept "the small predicate of being a pullback" Agda=is-pullback}}: given
the existence of the
[standard pullback type](foundation-core.standard-pullbacks.md) `A ×_X B`, we
can characterize pullback cones as those for which the gap map from the standard
pullback is an [equivalence](foundation-core.equivalences.md). This predicate is
a small [proposition](foundation-core.propositions.md) that we dub
{{#concept "the small predicate of being a pullback" Agda=is-pullback}}.
can characterize pullback cones as those for which the gap map into the standard
pullback is an [equivalence](foundation-core.equivalences.md).

## Properties

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