Hi jwass52!

The proof is difficult in the respect that it does not give you an open variable to work with, so I can definitely understand your frustration with it. I found it easier to do it under a conditional proof with a single indention. You could do it in a few less steps if you use a few nested proofs, but that ends up overcomplicating it and I don't know if you can use them or not for your class (assuming you are taking one for logic.) For this particular proof it is probably best to use a conditional proof rather than an indirect proof. This is not to say that indirect proof is not possible, in fact it may actually be a little bit easier but I find conditional proofs little easier to use especially considering the conclusion in this proof.

If you have any questions, just let me know, I'm happy to help out in any way I can.

I love doing indirect proofs

Here is the solution for that
1. ~(A v B) v ~(C v D)
2. (E v F) -> D
--------------------------
A -> ~E
3. ~(A -> ~E) (Assumption)
4. ~(~A V ~E) (Implication, 3)
5. A ^ E (De Morgans, 4)
6. E (Simplifcation, 5)
7. E V F (Addition, 6)
8. D (MP 2, 7)
9. A (Simplifcation, 5)
10. A V B (Addition, 9)
11. ~(C V D) (DS, 1, 11)
12. ~C ^ ~D (De Morgan's 11)
13. ~D (Simplifcation, 12)
14. D ^ ~D (Conjuction 8, 13)
Therefore
A -> ~E

Vid, do you use Paint for that or a specialized program?

I usually use paint to do the examples that I do. With paint, I have been able to get the right size where the picture does not get resized becuase of the restrictions on the forum. But the next time I do a proof I am going to try to use photoshop because all I have to do is make a proof template and insert the elements into the proof. I have one program from one of my logic books (Prospesel)that lets you input everything and it then formulates the format for you, but it is not really as good as doing it by hand.

This Post has been moved to another thread...