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: u_2 <-> p_4. p_6 or p_4. u_2 -> p. p_6 -> u_2.
p_6 -> p can be inferred via the transitivity rule. u_2 -> p_4 can be inferred via the biconditional elimination rule. p_4 -> u_2 can be inferred via the biconditional elimination rule.