6.5.15 Predicate calculus

Problem: An identically correct formula of predicate logic is the formula: 1. \( \exists x A(x) \Rightarrow \forall x B(x) \); 2. \( \forall x A(x) \Rightarrow \exists x A(x) \); 3. \( \forall x(A(x) \vee B(x)) \Rightarrow \forall x B(x) \); 4. \( \forall x A(x) \Rightarrow \exists x(A(x) \wedge B(x)) \).