Quotienting a Category by an Object: Explained

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In summary, quotienting a category by an object involves creating a new category where the objects are arrows that point to the specified object, and the arrows are commutative triangles with a designated vertex. Alternatively, it can be described algebraically as a category where the objects are arrows with a specified codomain and the arrows are defined by a specific relation between two arrows.
  • #1
fallgesetz
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What does it mean to quotient a category by an object of the category?

In particular, the problem in front of me specifies the category I ( a full subcategory of Top which is compact, contains coproducts, and the one point space), an object X of I, and asks me to do stuff with I/X.
 
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  • #2
This isn't a quotient, but a "slice category", a particular kind of "comma category".

Given any category E and object A, the category E/A is defined by:
. The objects of E/A are arrows of C of the form B --> A
. The arrows of E/A are commutative triangles of C with a distinguished vertex A (This arrow "points" in the same direction as the edge opposite A)

Or a more algebraic description
. Objects are arrows f of E such that codom(f) = A
. HomE/A(f,g) is the class of arrows h of E such that gh=f
 

FAQ: Quotienting a Category by an Object: Explained

What is quotienting a category by an object?

Quotienting a category by an object is a process in category theory where an object in a category is collapsed or "identified" with another object, resulting in a new category with fewer objects and morphisms.

Why is quotienting a category by an object useful?

Quotienting a category by an object allows for simplification of a category, making it easier to study and understand. It also helps to identify important relationships between objects in a category.

How is quotienting a category by an object different from taking a quotient in other mathematical areas?

In other mathematical areas, taking a quotient involves dividing one object by another, resulting in a smaller object. In category theory, quotienting involves collapsing or identifying objects, resulting in a smaller category.

Can any object in a category be quotiented?

No, not every object in a category can be quotiented. The object must have certain properties, such as being a zero object or having a universal property, for it to be quotiented.

Are there any important applications of quotienting a category by an object?

Yes, quotienting a category by an object has important applications in algebraic geometry, topology, and algebraic number theory. It also has applications in computer science, particularly in the study of abstract data types.

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