I still dont understand.If i have proved A/ \B in subproof B, then youre saying i should use V Intro, but thats not possible, because i have only proved one half of that subproof.I still need to show that i can derive A/\C from it as well, even when i prove in subproof C that A/ \C, thats only one half of the other half.

In other word to perform V Intro, i would have to prove that

C---> A/ \B i must still prove thsi to be allowed to perfrm v Intr

C---> A/ \C i get this part

B---> A/ \B i get this part

B---> A/ \C i must still prove this to be allowed to perfrm v Intr

Proof by cases as above.

So that both disjuncts derive the same conclusion in each instances.

Am i understanding this.

Thank you.