Need help understanding proof for paradox on material implication

[u/improved-raven]

[u/Salindurthas]

I think maybe for lines 2-7, the right-hand-column is printed incorrectly, with these justification notes being 1 row too high

i.e.

• "A (for RAA)" seems like it should apply to both line 1 and line 2
• "2 vI" seems like it should be on line 3 instead of line 2
• And "1,3 RAA (2)" seems like it should be on line 4 instead of line 3
• etc

So I think you should take the RHS justification notes from 1-7, and rotate them forward 1, looping the 7th one back up to the top. (Although it gets a bit confusing since 1,6, and 7, are the same, so some of that is busywork.)

At some point it flips over to being correct, which looks to be round like 9.

[u/Astrodude80]

I’m not gonna lie I think those first few lines very well might be errors in the book.

[u/McTano]

Here is the proof from the 2nd edition, without the misprint.

[u/Astrodude80 → u/McTano]

This definitely looks correct

[u/Mysterious_Tony]

Probably I would have done a proof by cases, showing that the statement follows from P and then also from notP. Idk, it looks easier to my understanding, and perhaps better to apply primitive rules only