# help with logical proofs using rules of inference.

1. Philosophy Forum
2. » Logic
3. » help with logical proofs using rules of inference.

Fri 27 Nov, 2009 04:57 pm
a kind person directed me here from the welcome threads to pose my questions for logic. i have a few problems that i have been boggling over within this week. each have to be solved using only the rules of inference. as obvious as it may be, i am very new to this and i am trying to understand. any help would be greatly appreciated!

1. O ⊃ P
P ⊃ ~P
__________
|- ~O

2. S /// (three-tier equal symbol) Q
~S
___________________
|- ~Q

3. T
__________
|- S ⊃ T

4. W . (X v Y)
~W v ~X
____________
|- W . Y

:perplexed:

Emil

Fri 27 Nov, 2009 05:07 pm
@mrmicr,
Don't you have a textbook? This is quite basic stuff and you should be able to figure it out simply by reading a textbook. I could do the proofs for you, but what would that help?

mrmicr

Fri 27 Nov, 2009 05:23 pm
@mrmicr,
that's just it, i don't understand the text book! i read the chapter and none of it makes sense. i am attempting to find a tutor i can contact. i understand your argument, however! i said "any help" so encouraging me to read perhaps falls under that category too.

Emil

Fri 27 Nov, 2009 05:42 pm
@mrmicr,
mrmicr;106473 wrote:
that's just it, i don't understand the text book! i read the chapter and none of it makes sense. i am attempting to find a tutor i can contact. i understand your argument, however! i said "any help" so encouraging me to read perhaps falls under that category too.

I can send you another textbook if you want. Just PM me your email.

mrmicr

Fri 27 Nov, 2009 08:23 pm
@Emil,
ok, i looked over my notes and skimmed the text book that you sent. please let me know if i'm on the right track with what i've done thus far.

1. O ⊃ P
2. P ⊃ ~P
3. ~P v ~P 2, impl
4. ~P 3, taut
5. ~O 1,4, mt

1. S <-> Q
2. ~S
3. (S ⊃ Q) & (Q ⊃ S) 1, equiv
4. (Q ⊃ S) & (S ⊃ Q) 3, com
5. Q ⊃ S 4, simp
6. ~Q 2,5, mt

1. T
2. T v ~S 1, add
3. ~S v T 2, com
4. S ⊃ T 3, impl

Emil

Sat 28 Nov, 2009 08:39 am
@mrmicr,
mrmicr;106522 wrote:
ok, i looked over my notes and skimmed the text book that you sent. please let me know if i'm on the right track with what i've done thus far.

1. O ⊃ P
2. P ⊃ ~P
3. ~P v ~P 2, impl
4. ~P 3, taut
5. ~O 1,4, mt

1. S <-> Q
2. ~S
3. (S ⊃ Q) & (Q ⊃ S) 1, equiv
4. (Q ⊃ S) & (S ⊃ Q) 3, com
5. Q ⊃ S 4, simp
6. ~Q 2,5, mt

1. T
2. T v ~S 1, add
3. ~S v T 2, com
4. S ⊃ T 3, impl

Symbols available here.

You are doing it correctly. :a-ok:

Though step (4) in proof (2) is redundant. You don't need to turn it around first to use simplification.

melissae2011

Mon 30 Nov, 2009 08:17 pm
@Emil,
I need help with a proof!:perplexed:

It was on my test today so I am just curious how to solve it. I pretty much know what I am doing, but this one has me stumped!:brickwall:

\$=existential
@=Universal

(\$xPx v \$xQx), @y(Py -> ~Ry) |- (@xRx -> \$xQx)

Can anyone help? I only know primitive rules.

Thanks!

Emil

Tue 1 Dec, 2009 01:33 am
@mrmicr,
Symbols available here.

1. Philosophy Forum
2. » Logic
3. » help with logical proofs using rules of inference.