A:
use B qw(bloh);
use C qw(bleh);
export = qw(blah);

<can use bloh and bleh>


B:
use C qw(bleh);
use A qw(blah);
export = qw(bloh);

<can use blah and bleh>

C:
use B qw(bloh);
use A qw(blah>;
export= qw(bleh);

<can use blah and bloh>