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_2 <-> s_2. ~t. s_2 -> t. q -> u_2.
~s_2 can be inferred via the modus tollens rule. u_2 -> s_2 can be inferred via the biconditional elimination rule. s_2 -> u_2 can be inferred via the biconditional elimination rule.