Every connective has Intro and Elim rules. But we also have a couple rules that don't go with connectives.
Reit is one of those rules. Reit means "reiteration." It allows you to repeat any previous line. All you have to do is repeat it exactly, and cite the line number you are reiterating.
Reit is a very helpful rule. For example, we know that P is equivalent to P&P.
That means we should be able to prove P&P from P. But &Intro requires us to cite two different lines. Let's see if you can use Reit to solve this problem.