Consider the following premises. forall y: S(y). T(f) <-> q_3. S(f) -> q_3. Can we infer q_3 from them? If possible, name the inference rules being used at each step.
 From forall y: S(y) we can infer forall y: S(y) or T(y) via universal addition. From forall y: S(y) or T(y) we can infer S(f) or T(f) via universal instantiation. From T(f) <-> q_3 we can infer T(f) -> q_3 via biconditional elimination. Finally, from S(f) -> q_3, T(f) -> q_3, S(f) or T(f) we can infer q_3 via disjunction elimination. Therefore, the answer is yes.