Originally Posted by under the clocks
Can I depart my country of origin, and then on return, use my 4 segments?
Yes. But what you can't do is pass back through your city of origin. The itinerary ends the first time you return to MEL. (Well strictly it ends the first time a ticket coupon finishes in MEL - in principle it is possible to pass through MEL if it is just a stop on a direct flight between two other places (e.g. ADL-HKG).)