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Hey people,
I don’t know if you all struggle with ND as much as I do. But I thought we could share some links, tutorials, videos or descriptions on how to do this. So we all master the technique

I found this video: https://www.youtube.com/watch?v=C30w5vZypXE The guy is strange, but the explanations help a lot I think. There are more videos about how to do Fitch style ND on his channel.

Greets.

I found that it was very very helpful for me to do the proofs of some basic logic concepts first, namely:

• Modus ponens: (( p → q ) & p ) → q
• Modus tollens; (( p → q ) & -q ) → -p
• Hypothetical syllogism: (( p → q ) & ( q → r )) → ( p → r )
• Disjunctive Syllogism: (( p | q ) & -p ) → q
• Addition: p → ( p & q )
• Comoposition: (( p → q ) & ( p → r )) → ( p → ( q & r ))

There are many more that you can find on the internet. The big aha came when I figured that I could use these proofs in other proofs. And then suddenly everything felt pretty easy.

Thank you very much luzi, they helped me as well! I think in the addition rule it should state (p v q) instead of (p & q). Gave me quite a cold sweat how to proof it until I found the “rule of addition” online

oh yes that is correct indeed. Sorry. You can find more formulas here https://en.wikipedia.org/wiki/Propositional_calculus#Basic_and_derived_argument_forms

I’m searching for nice PL1 ND problems to get used to that too.