If I am booking a multi-city trip in January, say

YYZ-LHR-YYZ-SYD-YYZ-LHR-YYZ

how many certs would I need? It says from origin to destination (including connections) however, would YYZ be the source and SYD be defined at the destination? Or would there be multiple desintations (LHR and SYD)

Either it's 2 certs, YYZ-SYD and SYD-YYZ or it's 4 certs YYZ-LHR, LHR-SYD, SYD-LHR and LHR-YYZ

This would all be booked as 1 ticket on AC.com multi-city booking....