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