How to Merge libraries using ar?

[Christoffer Gurell]

I would like to merge the contents of two libraries like:

ar rc l1.a o1.o o2.o ...
ar rc l2.a o3.o o4.o ...
ar rc l3.a l1.a l2.a

But this makes l3.a an archive containing two archives. 

Is there any way to do this?

 / Christoffer Gurell