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_1 -> s. t -> s_1. p_12 or t. p_12 <-> s_1.
t -> s can be inferred via the transitivity rule. p_12 -> s_1 can be inferred via the biconditional elimination rule. s_1 -> p_12 can be inferred via the biconditional elimination rule.