## Co/lax functors without apriori comparison cells

A profunctor is functorial iff every object of has a reflection in within . Fixing (arbitrarily) one reflection arrow for each object yields a functor such that .
Dually, is co-functorial iff every object of has a coreflection in , yielding a functor such that .
If both are satisfied, then above is left adjoint to .

This analogy continues in dimension 2 (for bicategories or double categories), yielding the colax functors as double profunctors with the reflection property and the lax functors as double profunctors with the coreflection property. If a double profunctor has both property, it determines a colax/lax adjunction.

## What is a profunctor?

Recall that a category is a directed graph equipped with an associative and unital composition of its edges. In the categorical context, the nodes of the graph are also called objects and edges are called arrows or morphisms. The unitality requirement says that each object has a unit arrow , called identity, which doesn’t affect the result of the compositions.

A functor is a composition and identity preserving graph morphism from a category to a category.

A profunctor, on the other hand, connects up two categories by (potentially) adding more morphisms in between them ‘from the outer world’. In other perspective, we can describe this setting as one of the two categories acting from the left and the other one acting from the right on the newly added morphisms. This can also be grasped as simply being a two variable functor to the category of sets, contravariant in the first argument.
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## Functor as a fibration

In topology, any continuous function can be considered as a fibration over space , with total space , where the fibres are glued together according to the topology of .

Likewise, any functor can be regarded as a kind of fibration over . Each object determines a fibre category with arrows which are mapped to .

In this generality, the fibres connect up by means of profunctors between them and then and the original composition of are encapsulated in the arising mapping .
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## On the two definitions of adjunctions

(Note that we write compositions from left to right and accordingly apply most maps on the right.)

Def.1
A functor is called a left adjoint to a functor if there is a bijection between the homsets: natural in both and . In this case is called a right adjoint to , and we write .

Def.2
A functor is called a left adjoint to a functor if there are natural transformations and satisfying the zig-zag identities: So, why are these two definitions equivalent?

## Morita equivalence by categorical bridges

Let denote the category of 2 objects (name them ) and 2 nonidentity arrows, which are inverses of each other.

We define a  bridge  as a category over , i.e. a category equipped with a functor . The full subcategories and are called banks of the bridge, and we write .
The arrows in the -preimage of the two arrows in are referred to as through arrows or heteromorphisms in the bridge.
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## Situation-Tree Logic on a Profunctor

Let be a given profunctor. We regard it as a category, fully containing both and , with additional heteromorphisms .
Objects of will be regarded as abstract situations (we are given this and that perhaps with certain elementary conditions), objects of will be called models, and a heteromorphism is regarded as an interpretation of situation in model .
Continue reading “Situation-Tree Logic on a Profunctor”