Given (p ∧ q), use the Fitch system to prove (q ∨ r).

Question

I know this question has already been posted but I cannot seem to find an answer there.I am taking this course and I just cannot figure out how to solve this on the platform. Please I really need help with this. The link to the platform is: http://intrologic.stanford.edu/exercises/exercise_04_02.html.

Thanks in advance I would trully be grateful to the person who tells me how to solve this on the given website. Thanks in advance!

Possible duplicate of Given (p ∧ q), use the Fitch system to prove (q ∨ r) — tien lee, Jul 14 '18 at 14:47
See http://www.dcproof.com/MIParadox5.htm It's my own system of logic (FOL-ish), but it you should be able to easily translate into any form of classical logic. — Dan Christensen, Jul 14 '18 at 21:29
Also: Look at the page you linked to, find on it the button which says "Show Answer", and click that. — Graham Kemp, Jul 15 '18 at 09:05

score 0 · Answer 1 · answered Jul 14 '18 at 15:26

This is really easy ... so I figure it must be your first formal proof and I know the learning curve for these formal proofs can be pretty steep, so here are a few pointers:

Look at the main operator of any of your premises, and see if you can apply the corresponding Elimination rule

In your case, you have $p \land q$, so the main operator is $\land$ ... so can you apply $\land$ Elimination on that statement?

Look at the main operator of any of the statements that you are trying to get, and see if you can apply the corresponding Introduction rule

In your case, you want $q \lor r$, so the main operator is $\lor$ ... so can you apply $\lor$ Introduction on some statement to get $q \lor r$> ... which means you need either $q$ or $r$ by itself?

Given (p ∧ q), use the Fitch system to prove (q ∨ r).

1 Answers1