Ah our old foe, OAS. A concept that has caused numerous confusions from my days as a Level 1 candidate. Each year, I merely memorise some facts about it, enough to get over the line.
This year I finally want to understand this thing.
Can someone please give as simple an explanation as possible of the OAS, how it relates to Z spread and when given a table of OAS. Z etc how we determine whether it is callable or puttable.