Which of the following propositional forms are tautologies.

(p implies (q implies r)) implies ((p and not q) or r)

(p and not q) or (q and not r) or (r and not p)

I need help in both questions, btw, simplify only, no truth table

Thanks!

Printable View

- Sep 4th 2013, 09:39 PMjoseph1125Need help on mathematical logic
Which of the following propositional forms are tautologies.

(p implies (q implies r)) implies ((p and not q) or r)

(p and not q) or (q and not r) or (r and not p)

I need help in both questions, btw, simplify only, no truth table

Thanks! - Sep 5th 2013, 07:19 AMemakarovRe: Need help on mathematical logic
Can you determine whether they are tautologies using other means? How do you prove that something is

*not*a tautology using simplifications? - Sep 5th 2013, 10:52 AMHartlwRe: Need help on mathematical logic
Assume Definition of tautology: Statement that is

__always__true.

Write first one as A->B and let p=q=r=F

Then A is F and B is F so A->B is False. Not a tautology.

Write second one as AorBorC and let p=q=r=F. Then A,B and C are false so AorBorC is false. Not a tautology.