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 -> s_1. r_3 or t_4. s_1 <-> t_4. r_3 -> p.
r_3 -> s_1 can be inferred via the transitivity rule. s_1 -> t_4 can be inferred via the biconditional elimination rule. t_4 -> s_1 can be inferred via the biconditional elimination rule.