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: u_1 <-> s. p_2 -> u_1. ~s. u_1 -> p_2.
p_2 <-> u_1 can be inferred via the biconditional introduction rule. u_1 <-> p_2 can be inferred via the biconditional introduction rule. u_1 -> s can be inferred via the biconditional elimination rule. s -> u_1 can be inferred via the biconditional elimination rule. ~u_1 can be inferred via the biconditional elimination rule.