Consider the following premises. forall y_1: T_1(y_1). forall y_1: T_1(y_1) <-> T_4(y_1). Can we infer forall y_1: T_4(y_1) from them?
 From forall y_1: T_1(y_1) <-> T_4(y_1) we can infer forall y_1: T_1(y_1) -> T_4(y_1). Finally, from forall y_1: T_1(y_1) -> T_4(y_1), forall y_1: T_1(y_1) we can infer forall y_1: T_4(y_1). Therefore, the answer is yes.