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natural_transformation [2014/08/01 13:59] nikolaj |
natural_transformation [2016/04/09 15:00] nikolaj |
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==== Collection ==== | ==== Collection ==== | ||
| @#55CCEE: context | @#55CCEE: $F,G$ in ${\bf C}\longrightarrow{\bf D}$ | | | @#55CCEE: context | @#55CCEE: $F,G$ in ${\bf C}\longrightarrow{\bf D}$ | | ||
- | | @#FFBB00: definiendum | @#FFBB00: $\eta$ in $\mathrm{nat}(F,G)$ | | + | | @#FFBB00: definiendum | @#FFBB00: $\eta$ in $F\xrightarrow{\bullet}G$ | |
| @#AAFFAA: inclusion | @#AAFFAA: $\eta:{\large\prod}_{(A:\mathrm{Ob}_{\bf C})}F\,A\to G\,A$ | | | @#AAFFAA: inclusion | @#AAFFAA: $\eta:{\large\prod}_{(A:\mathrm{Ob}_{\bf C})}F\,A\to G\,A$ | | ||
| @#55EE55: postulate | @#55EE55: @#88DDEE: $\eta\circ F(\,f)=G(\,f)\circ\eta$ | | | @#55EE55: postulate | @#55EE55: @#88DDEE: $\eta\circ F(\,f)=G(\,f)\circ\eta$ | | ||
+ | Here, in the postulate, I've left the components ($\eta_A,\eta_B$ etc.) implicit. | ||
==== Discussion ==== | ==== Discussion ==== | ||
- | For any $A:\mathrm{Ob}_{\bf C}$, we write $\eta_A$ for the map $F\,A\to G\,A$. This is called the //component// of the natural transformation $\eta$ at $A$. | + | === Idea === |
+ | Natural transformation form a collection of arrows within a single category which are compatible with the (structure preserving) functors. | ||
+ | === Elaboration === | ||
If one thinks about it for a minute, the data provided with a natural transformation can in fact be reformulated as just another functor, namely in ${\bf C}\times(\bullet\to\bullet)\longrightarrow{\bf D}$. This mirrors a homotopy. | If one thinks about it for a minute, the data provided with a natural transformation can in fact be reformulated as just another functor, namely in ${\bf C}\times(\bullet\to\bullet)\longrightarrow{\bf D}$. This mirrors a homotopy. | ||
+ | |||
+ | === Notation === | ||
+ | For any $A:\mathrm{Ob}_{\bf C}$, we write $\eta_A$ for the map $F\,A\to G\,A$. This is called the //component// of the natural transformation $\eta$ at $A$. | ||
=== Reference === | === Reference === |