One of the De Morgan's laws states ¬(p ∧ q) ≡ ¬p ∨ ¬q . Does that also apply to three propositions p, q, and r for example? Like would ¬(p ∧ q ∧ r) ≡ ¬p ∨ ¬q ∨ ¬r work?
yes. Think about it
p^q^r is true only if all three are true
so, ¬(p^q^r) is true if any one of them is false.