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_3 <-> u. u or p_1. p_3 -> u. p_1 -> p_3.
p_1 -> u can be inferred via the transitivity rule. p_3 -> u can be inferred via the biconditional elimination rule. u -> p_3 can be inferred via the biconditional elimination rule.