Consider the following premises. forall y: R(y) -> T(y). exists y: Q_3(y). forall y: T(y) <-> Q_3(y). Can we infer exists y: T(y) from them? If possible, name the inference rules being used at each step.
 From exists y: Q_3(y) we can infer exists y: Q_3(y) or R(y) via existential addition. From forall y: T(y) <-> Q_3(y) we can infer forall y: Q_3(y) -> T(y) via universal biconditional elimination. Finally, from forall y: Q_3(y) -> T(y), forall y: R(y) -> T(y), exists y: Q_3(y) or R(y) we can infer exists y: T(y) via existential disjunction elimination. Therefore, the answer is yes.