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_2 <-> u. u <-> q. ~p_1. p_1 <-> u_2.
u_2 -> u can be inferred via the biconditional elimination rule. u -> q can be inferred via the biconditional elimination rule. p_1 -> u_2 can be inferred via the biconditional elimination rule. u -> u_2 can be inferred via the biconditional elimination rule. q -> u can be inferred via the biconditional elimination rule. u_2 -> p_1 can be inferred via the biconditional elimination rule. ~u_2 can be inferred via the biconditional elimination rule.