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: r. t or s_2. t -> p_13. p_13 <-> s_2.
p_13 -> s_2 can be inferred via the biconditional elimination rule. s_2 -> p_13 can be inferred via the biconditional elimination rule.