When you’re working on the natural deduction proofs for PS2, it might be helpful to consider rewriting a formula uses a logical equivalence. For example, there is an equivalence between p–>q and ~p v q. However, if you use something like this, you must also show a side proof that the equivalence is correct. That is, you should show that you can assume each of the sides and prove the other. If you do that, you will receive full credit for the use of that rule. However, if you use a logical equivalence that isn’t one of the specific rules given in the book without showing that it is valid, only partial credit will be given.