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: r <-> t. ~r_1. ~t. r_1 <-> q_7.
~r_1 and ~t can be inferred via the conjunction rule. ~t and ~r_1 can be inferred via the conjunction rule. r -> t can be inferred via the biconditional elimination rule. r_1 -> q_7 can be inferred via the biconditional elimination rule. t -> r can be inferred via the biconditional elimination rule. q_7 -> r_1 can be inferred via the biconditional elimination rule. ~q_7 can be inferred via the biconditional elimination rule. ~r can be inferred via the biconditional elimination rule.