Types
and Examples of Categories |

**General Types**

* __Single spaces as categories__:
Any set with a relation is a category, with relations as arrows; For example,
a poset.

* __Thin__: One for which each Hom-set contains at most one element; For example,
a poset.

* __With terminal element__: One with an object to which there is an arrow
from every other object; For example, Set.

* __Tensor categories__:
Types are spherical, ribbon, symmetric; > s.a. lattice
gauge theory.

* __Remark__: Some categories
are modeled after other ones; For example, manifolds are modeled after finite-dimensional
vector spaces.

@ __Other types__: Neeman Top(98)
[non-compactly generated]; Jacobs a1101 [dagger categories of tame relations].

> __Online resources__: see Wikipedia page.

**Examples**
s.a. category theory [generalizations]; categories in physics [categories of relations, applications].

* __Set__: The category of sets and mappings between sets.

* __Top__: The category of topological spaces,
with continuous maps as morphisms; The composition is composition of maps.

* __Grp__: The category of groups, with homomorphisms
as morphisms; Composition is composition of maps; A monomorphism is a 1-1 homomorphism *f*:
Ker(*f*) = *e* (the identity).

* __Hilb__: The category of Hilbert spaces
and bounded linear operators, used in quantum mechanics.

* __Man__: The category of differentiable manifolds and differentiable maps.

* __nCob__: The category of manifolds (= spacelike hypersurfaces) and *n*-dimensional
cobordisms, used in general relativity.

* __Prop__: A strict symmetric monoidal category where the objects are natural numbers, with the tensor product of objects given by addition.

* __Vec__: The category of vector spaces, a monoidal tensor category.

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24 dec 2017