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: q -> r_1. q or ~r_1. p <-> q. ~p.
r_1 -> q can be inferred via the rewriting rule. p -> q can be inferred via the biconditional elimination rule. q -> p can be inferred via the biconditional elimination rule. ~q can be inferred via the biconditional elimination rule.