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_6 -> p_13. u_1 -> r_1. p_13 <-> u_1. r_1 -> r_6.
u_1 -> r_6 can be inferred via the transitivity rule. r_1 -> p_13 can be inferred via the transitivity rule. p_13 -> u_1 can be inferred via the biconditional elimination rule. u_1 -> p_13 can be inferred via the biconditional elimination rule.