Originally Posted by
petez
do the rules permit LHR-JFK-LAX-DOH-HKG-SYD-PER-LHR
I don't think so, because you'd be backtracking across the Atlantic, re-entering Europe/Middle East after touching North America. There are some exceptions that allow you to re-enter a continent, such as hitting North America twice if once is to or from South America, or hitting Asia twice if once is for travel between Europe and Australia/Pacific.