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_4 <-> ~t. t <-> q_1. ~q_1.
u_4 -> ~t can be inferred via the biconditional elimination rule. t -> q_1 can be inferred via the biconditional elimination rule. ~t -> u_4 can be inferred via the biconditional elimination rule. q_1 -> t can be inferred via the biconditional elimination rule. ~t can be inferred via the biconditional elimination rule.