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: s -> q_4. q_4 -> p_6. p_6 -> q_4.
s -> p_6 can be inferred via the transitivity rule. q_4 <-> p_6 can be inferred via the biconditional introduction rule. p_6 <-> q_4 can be inferred via the biconditional introduction rule.