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 -> p. p -> r_2. p_6 <-> u.
p_6 -> r_2 can be inferred via the transitivity rule. p_6 -> u can be inferred via the biconditional elimination rule. u -> p_6 can be inferred via the biconditional elimination rule.