What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? s_3 -> t_4. s_3 -> t_4. ~s_3. t_4 -> s_3.
~t_4. s_3 <-> t_4. s_3 <-> t_4. t_4 <-> s_3. t_4 <-> s_3.