RC corners used for setup and hold violations

For setup:
cw  ==> for shorter nets, optimistic compared to rcw;  extraction takes less time compared to rcw.
rcw  ==> used for longer nets, contributes more delay (worst)

   cw is used at the early stage for setup fixes but rcw is used at the final sign-off.

For hold:
cb  ==> best and optimistic for hold,
rcb  ==> we never use this combination.