I would like to make a TikZ diagram to show the detailed dependency structure of the theorems in my thesis with nodes and subnodes. Ex:
Theorem 4 (A)
coding theorem (A1)
proof techniques (A1a)
converse (A2)
Theorem 5 (B)
and then indicate that there is a dependency
(A1a) --> (B)
which is more precise than saying that Theorem 5 depends on Theorem 4. More specifically, this is what I am trying to draw:

Is there a TikZ package for that? Or for drawing .deb dependency graphs?
I found one package/framework for course prerequisites: http://www.texample.net/tikz/examples/prerequisite-chart/ but the underlying format is very low level so you are meant to edit with a program.
All advice / example / recommendations will be much appreciated!
[tikz-pgf] graph. That would search the graph in only TikZ tagged questions. – percusse Mar 30 '12 at 20:54