Logic: (p implies q) or (q implies r)

[sombrancelha]

Homework Statement

I've started studying natural deduction recently and I have to prove

(p implies q) or (q implies r)

Homework Equations

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The Attempt at a Solution

I thought about using the Law of Excluded Middle, but I'm not sure.

 

[lanedance]

isn't that only one side of an expression - what do you have to prove?

 

[sombrancelha]

That's what I have to prove. There are no premisses.

 

[lanedance]

could just be me, but still not getting it... usuallly you have something like, "knowing A, prove B" but you just have B?

do you mean you need to simplify or expand the expression?

 

[Mark44]

I believe that you are supposed to show that the given expression is a tautology. IOW, an expression that is true for all values of p, q, and r. A simple way to do this is to make a truth table with 8 rows, one for each of the possible truth values for p, q, and r.