Homework: radixvm question

Submit two items to the the submission web site:

Answer the following question: Refcache re-examines the reference count of an object two epochs later after it inserts the object in a per-core review queue (see page 4, 2nd paragraph, right column). What goes wrong if refcache reviews objects only one epoch later? Is two epochs later just more efficient or is it necessary for correctness? (Briefly explain your answer.)