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 or s_2. s_2 <-> t. t -> p. p_6 -> t.
p_6 -> p can be inferred via the transitivity rule. s_2 -> t can be inferred via the biconditional elimination rule. t -> s_2 can be inferred via the biconditional elimination rule.