How to express inter-directory dependencies in <bsd.*.mk> infrastructure?

[Lev Serebryakov]

Hello, Hackers.

  (SORRY FOR SENDING INCOMPLETE MESSAGE)

  How to express inter-directory dependencies in <bsd.*.mk> infrastructure?

  I have project, which has two subdirectories: "lib" and "bin".
 Top-level Makefile is simple one, looks like this:

===================================
SUBDIR= lib \
        bin

.include <bsd.subdir.mk>
===================================

 "lib" subdirectory has Makefile with "<bsd.lib.mk>" included, and
 "bin" -- with <bsd.prog.mk> included.

 But how could I express, that PROG in bin depends on LIB from lib, to
cause rebuilding of PROG when LIB is changed (when I call "make" on
top level)?

-- 
// Black Lion AKA Lev Serebryakov <lev at FreeBSD.org>