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_1. p -> u_1. p.
u_1 can be inferred via the modus ponens rule. u_1 -> s_1 can be inferred via the biconditional elimination rule. s_1 -> u_1 can be inferred via the biconditional elimination rule.