Interface of the R-tree in order to work with postgresql

Hi everybody!
I'm Jorge from Peru South America, and this is my first post

I want to know how can I add a new spatial access method into the postgresql
(I'm doing research on spatial access methods( reading a lot of papers and
programming a lot too ) but also I want to know how can I add my new data
structure( if someday i get it, of course =) ) in the postgresql, I mean
where can i find the .h that describes the interface that a spatial access
method, like the R-tree, must have in order to work with postgresql.

I think that to understand how postgresql works with spatial access methods,
like the R-tree, I need to find a .h or .c to begin
reading the code, so can you tell me where to start?

I hope you can help me
regards Jorge