What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: forall x_12: P_12(x_12) <-> Q_12(x_12). P_12(a_1).
exists x: P_12(x) can be inferred via the existential generalization rule. forall x_12: P_12(x_12) -> Q_12(x_12) can be inferred via the universal biconditional elimination rule. forall x_12: Q_12(x_12) -> P_12(x_12) can be inferred via the universal biconditional elimination rule.