[Automake] library dependencies?

[Stig S. Bakken]

There's one thing that has been nagging me about automake for a while:
how do you express dependencies to a library in the same package?  For
example, if my "hello" program links with "libdoo.a" from another
directory, how do I make "hello" re-link if libfoo.a changes without
adding a lot of rules manually?

This question appears to me as a FAQ, but I have not been able to find
any references to it.

 - Stig