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 -> u_4. u_4 -> p. u. p.
u_4 can be inferred via the modus ponens rule. u and p can be inferred via the conjunction rule. p and u can be inferred via the conjunction rule. p <-> u_4 can be inferred via the biconditional introduction rule. u_4 <-> p can be inferred via the biconditional introduction rule.