How to Derive ((A>B)>A)>A Using Sentential Logic?

[Cornelius]

1. How do you prove, using SD, that ((A>B)>A)>A?


3. I tried to first assume (A>B)>A. Then I made a sub-derivation, assuming ~A. In this sub-derivation, I need to derive a contradiction. How?

 

[cristo]

What does your symbol ">" mean?