In this Wikipedia page https://en.wikipedia.org/wiki/Propositional_calculus, specifically in the section "Example 2. Natural deduction system", it mentions 11 inference rules and no axioms for a natural deduction system. I wanted to know how we can prove the following formulas using only the 11 rules mentioned in that page:
- ¬A∨A
- ¬(¬A∧A)
- (A→¬A)→¬A
- A→(B→C) → (A∧B)→C
And most importantly, please show all of that using a sequence of numbered lines, instead of any tree-proofs or diagrams.
The first three all have a similar technique to use, so I’ll just prove $A \lor \neg A$. The last one should be fairly easy.
Note that this system requires you to use rules for other operators to prove things for negation, reiteration, etc. The general strategy is the same as for a simpler ND system, but you just have to translate those rules to these ones.