How to prove Distractive dilemma ?

1. Aug 7, 2013

phydis

[ [(p-->q) and (r-->s)] and (~q or ~s) ] --> (~p or ~r)

I know all basic theories in Logic and I want to know the correct way/correct steps of proving this kind of things? I'm a beginner.. please help

I can explain above dilemma in words, but I have no idea how to write down the proof correctly.

2. Aug 8, 2013

Stephen Tashi

There isn't a single standard for doing proofs that is correct. In a logic course, you would be given certain permissible patterns to use in a proof and you would naturally be expected to use them. (It's also taught in logic courses that proofs can be done by using truth tables.) If this problem arose in a discussion in a calculus course, it would probably be acceptable to offer a proof in words. You have to explain in what context you wish to give a proof.

Also, I don't think the names of proof techniques used in logic books are completely standardized, so a person might have to be familiar with the book or materials you are using in order to advise you.

3. Aug 8, 2013

verty

Proving it by contradiction may be the easiest way. See if you can do that.