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: ~p_5. p_5 <-> u_1. p_1 -> u_1. u_1 -> p_1.
p_1 <-> u_1 can be inferred via the biconditional introduction rule. u_1 <-> p_1 can be inferred via the biconditional introduction rule. p_5 -> u_1 can be inferred via the biconditional elimination rule. u_1 -> p_5 can be inferred via the biconditional elimination rule. ~u_1 can be inferred via the biconditional elimination rule.