p ∧ ¬p $\vdash$ q ∧ ¬q
p ∧ r ⇒ q ∧ r , p ∨ r ⇒ q ∨ r $\vdash$ p ⇒ q
I have literally been trying to figure these out all morning and I'm desperately stuck now. We have to prove them using propositional logic via the formal proof/natural deduction system. If anyone could help me out and explain how they reach their conclusion I'd be immeasurably grateful - thanks.
The ruleset used for this include:
and-elimination and-introduction or-elimination or-introduction <=>-introduction <=>-elimination =>-introduction =>-elimination ¬-introduction ¬-elimination
Hint
For the second one, assume $p$ and derive $p \lor r$ by $\lor$-intro.
Then derive $q \lor r$ from the second premise.
Now we have to consider $q \lor r$ for $\lor$-elim.
From the "alternative" $q$, we have immediately $p \to q$.
From the alternative $r$ we get $p \land r$ and thus $q \land r$ from the first premise.
Now apply $\land$-elim to derive $q$ and then $p \to q$ again.
Thus, we may conclude by $\lor$-elim.