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_6 <-> r_2. ~r_4. r_4 -> p_6. p_6 -> r_4.
~p_6 can be inferred via the modus tollens rule. r_4 <-> p_6 can be inferred via the biconditional introduction rule. p_6 <-> r_4 can be inferred via the biconditional introduction rule. p_6 -> r_2 can be inferred via the biconditional elimination rule. r_2 -> p_6 can be inferred via the biconditional elimination rule.