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: t -> q. ~t. q -> t. q -> t.
~q can be inferred via the modus tollens rule. ~q can be inferred via the modus tollens rule. t <-> q can be inferred via the biconditional introduction rule. t <-> q can be inferred via the biconditional introduction rule. q <-> t can be inferred via the biconditional introduction rule. q <-> t can be inferred via the biconditional introduction rule.