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 -> p_1. ~u -> s_1. p <-> p_1. ~p.
p -> p_1 can be inferred via the biconditional elimination rule. p_1 -> p can be inferred via the biconditional elimination rule. ~p_1 can be inferred via the biconditional elimination rule.