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: s or s_4. q_1 <-> s. q_1 <-> r_4. ~r_4.
q_1 -> s can be inferred via the biconditional elimination rule. q_1 -> r_4 can be inferred via the biconditional elimination rule. s -> q_1 can be inferred via the biconditional elimination rule. r_4 -> q_1 can be inferred via the biconditional elimination rule. ~q_1 can be inferred via the biconditional elimination rule.