Header autonumbering help needed

Question

I am using FrameMaker v7.1p114 and I would like to create headings and subheadings within book chapters that have auto numbering such as the following assuming that this is Chapter 5:
5.1 Main heading 1
5.1.1 Sub heading 1
5.1.2 Sub heading 2
5.2 Main heading 2
5.2.1 Sub heading 1
5.2.2 Sub heading 2
I believe that I have the main heading figured out by using a paragraph format that uses the autonumber format as follows: <$chapnum>.<n+>iu
However, in order to get the desired autonumbered sub heading, what is a good method?  One method that should work, but that requires me to create a lot of paragraph definitions, and that is not a completely autonumbered solution is as follows:
* create as many paragraph definitions as sub headings needed
* just put the <n+> on the end
For example, I could create a subheading #1 as: <$chapnum>.<n=1>.<n+>
a subheading #2 as: <$chapnum>.<n=2>.<n+>
a subheading #3 as: <$chapnum>.<n=3>.<n+>
The problem is that if I insert/move one of the sub headed sections, I would have to manually change the paragraph format and then go through the document and correct any text referenences that mention the specific section that now has a new sub heading number.

Answer 1

I used Dan's paper to create a test file in about 10 minutes and believe that I have come up with a solution.  I crated 3 paragraph definitions and the code is as follows:
5.1    main 1-1    H:<$chapnum>.<n+>< =0>
5.1.1    sub 1-1-1  H:<$chapnum>.<n>.<n+>< =0>
5.1.1.1   sub 1-1-1-1  H:<$chapnum>.<n>.<n>.<n+>< =0>
5.1.1.2   sub 1-1-1-2
5.1.2    sub 1-1-2
5.1.3    sub 1-1-3
5.1.1.3.1   sub 1-1-3-1
5.1.3.2   sub 1-1-3-2
5.2  main 2
5.2.1  sub 1-2-1
5.2.1.1  sub 1-2-1-1
5.2.1.2  sub 1-2-1-2
I should have been using FrameMaker years ago .