Consider the following premises. forall z: ~T(z). t_4 <-> s_1. t_4 <-> T(d_2). Can we infer ~s_1 from them? If possible, name the inference rules being used at each step.
 From forall z: ~T(z) we can infer ~T(d_2) via universal instantiation. From t_4 <-> T(d_2), ~T(d_2) we can infer ~t_4 via biconditional elimination. Finally, from t_4 <-> s_1, ~t_4 we can infer ~s_1 via biconditional elimination. Therefore, the answer is yes.