Re: Need help with a simple logic proof.

On 7 Mar 2007 16:45:02 -0800, xaceri@xxxxxxxxxxx wrote:


I've tried everything I can think of, I just can't get this conclusion
from these premises. Here's the problem:

1. L->M
2. N->O
C. L v N -> M v O


Here's a proof in some standard system of natural deduction.

1 (1) L -> M A
2 (2) N -> O A
3 (3) L v N A
4 (4) L A (first disjunct of L v N)
1,4 (5) M 1,4 ->E (MP)
1,4 (6) M v O 5 vI
7 (7) N A (second disjunct of L v N)
2,7 (8) O 2,7 ->E (MP)
2,7 (9) M v O 8 vI
1,2,3 (10) M v O 3,4,6,7,9 vE
1,2 (11) L v N -> M v O 3,10 ->I (CP)


F.

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