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Viewing Version 2 of 'category example (arrow category)'
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Title of object: category example (arrow category)
Canonical Name: ExampleOfCategory
Type: Example

Created on: 2002-06-01 08:56:32-04
Modified on: 2002-06-02 07:00:08-04

Creator: n3o
Modifier: n3o
Author: n3o

Classification: msc:18A05

Preamble:

% this is the default PlanetMath preamble. as your knowledge
% of TeX increases, you will probably want to edit this, but
% it should be fine as is for beginners.
% almost certainly you want these
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}
% used for TeXing text within eps files
%\usepackage{psfrag}
% need this for including graphics (\includegraphics)
%\usepackage{graphicx}
% for neatly defining theorems and propositions
%\usepackage{amsthm}
% making logically defined graphics
%\usepackage{xypic}
% there are many more packages, add them here as you need them
% define commands here
Content:

Let $\mathcal{C}$ be a category, and let $\mathcal{D}$ be the category whose objects are the arrows of $\mathcal{C}$. A morphism between two morphisms $f: A \rightarrow B$ and $g: A' \rightarrow B'$ is defined to be a couple of morphisms $(h,k)$, where $h \in \hom(A,A')$ and $k \in \hom(B,B')$ such that $g \circ h = k \circ f$. The resulting category $\mathcal{D}$ is called the \emph{arrow category} of $\mathcal{C}$.