How to merge two “ar” static libraries into one?

Question

I have 2 static Linux libraries, created by ar cr, libabc.a and libxyz.a.
I want to merge them into one static library libaz

Answer 1

ar crsT libaz.a libabc.a libxyz.a

Here, you create archive of archives and then 'flatten' (thinning) result with T flag. Not sure how it'll work with same name .o files that might be contained within.