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: u_4 <-> p. p <-> p_1. ~u_4. q_1.
~u_4 and q_1 can be inferred via the conjunction rule. q_1 and ~u_4 can be inferred via the conjunction rule. u_4 -> p can be inferred via the biconditional elimination rule. p -> p_1 can be inferred via the biconditional elimination rule. p -> u_4 can be inferred via the biconditional elimination rule. p_1 -> p can be inferred via the biconditional elimination rule. ~p can be inferred via the biconditional elimination rule.