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_9 <-> p. p_9 or ~p.
p -> p_9 can be inferred via the rewriting rule. p_9 -> p can be inferred via the biconditional elimination rule. p -> p_9 can be inferred via the biconditional elimination rule.