What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: r_1 <-> s_3. r_1 -> s_3. s_4 <-> r_1. ~s_3.
~r_1 can be inferred via the modus tollens rule. r_1 -> s_3 can be inferred via the biconditional elimination rule. s_4 -> r_1 can be inferred via the biconditional elimination rule. s_3 -> r_1 can be inferred via the biconditional elimination rule. r_1 -> s_4 can be inferred via the biconditional elimination rule. ~r_1 can be inferred via the biconditional elimination rule.