Explicit requirement to use classical logic for section 2 exercises somewhat implies that section 1 exercises are meant to be proven constructively, which contradicts the section 3 suggestion to prove ¬(p ↔ ¬p) (listed under 1) without using classical logic.
Explicit requirement to use classical logic for section 2 exercises somewhat implies that section 1 exercises are meant to be proven constructively, which contradicts the section 3 suggestion to prove
¬(p ↔ ¬p)
(listed under 1) without using classical logic.