Whoops: Those ascii diagrams again:
+---------------+
| +-------+ |
JACK ----->|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+
+-------+
| |
+---|<- C <-|<--+
| | | |
| +-------+ |
| |
| +-------+ |
JACK ----->|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+
(also available as an attachment)
+---------------+
| +-------+ |
JACK ----->|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+
+-------+
| |
+---|<- C <-|<--+
| | | |
| +-------+ |
| |
| +-------+ |
JACK ----->|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+