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. p <-> s_4.
p <-> u_4 can be inferred via the biconditional introduction rule. u_4 <-> p can be inferred via the biconditional introduction rule. p -> s_4 can be inferred via the biconditional elimination rule. s_4 -> p can be inferred via the biconditional elimination rule.