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 <-> r. s -> r. p <-> u.
p -> r can be inferred via the biconditional elimination rule. p -> u can be inferred via the biconditional elimination rule. r -> p can be inferred via the biconditional elimination rule. u -> p can be inferred via the biconditional elimination rule.