uppose we made it this far into the proof and we were not quite sure what to do next.

We can always look at the aim box and the assumptions we've already made as a way to help us figure out what to do next. In this case, if we look at our current aim, that will prompt us for what to do on Line $3.$

What wff should we write in on Line $3,$ given our current aim?

$1(1)(($R & T$)->$ S$)$ A Aim:

$(($T $->$ R$)->($R $->$ S$))$

$($R $->$ S$)$

$2(2)($T $->$ R$)$ A$/$CP $($R $->$ S$)$

Remember $-$ Formatting will be important here! So$,$ enter your wff according to the following conventions: