Showing posts with label Happy. Show all posts
Showing posts with label Happy. Show all posts

Sunday, January 5, 2014

The Blink...

The Blink...
Delved eyes intertwined, fractionally unbreakable hold, (just for a second)!;
iiiiiiinside I see, .. see, …. 
sea;
the sea I fall into…
…and.„„
eye Saw the universe;



Delved eyes intertwined, fractionally unbreakable hold, (just for a second)!;
iiiiiiinside I see, .. see, ….
sea;
the sea I fall into…
…and.„„
I saw nothing.

Wednesday, May 8, 2013

Functor Categories as Topoi

Consider the category of functors between two categories $E:=D^C$, with D being Sets.  It may be shown that E is complete and co-complete due to the fact Sets is; thinking of each object in E as a map from C to Sets, in the sense of evaluation, it can be shown that $(\varinjlim F_i) (C)= \varinjlim F_i(C)$ where $F_i$ are objects in E.  In particular $-\times E: E \rightarrow E$ commultes with both types of limits.  

Essentially E inheriting Sets' properties, similarly it can be shown that it is abelian, with enough injective objects (again see See Tamme).   
On objects A of E, PE(A) defined to be the set of subfunctors $Hom_E(-,A)xE$ is a functor with values in E, and the subfunctors FxE are in bijection with the morphisms in Nat(F,PE).  Hence E is a topos.  

The Functor category E as described above is called a presheaf, and in the case of a locally small category, via a Yoneda Embedding it may be though of as enlarging an arbitrary category C in such a way, that the enriched C will be complete, co-complete, abelian and posses enough injectives.  

Monday, May 6, 2013

A little soundscaping....