As you may note when you look at the solutions to homework 10, I
derived biconditionals from the pair of conditionals they are equivalent
to, and I used CP to derive each of the conditionals. That is a standard
way to go about deriving a biconditional. Take (P <-> Q), for instance. To
derive this, you can derive (P -> Q) by CP and (Q -> P) by CP. You can then
use Equiv. to derive (P <-> Q).