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: Charles is poor if and only if Barbara is rich. Barbara is not rich. If Charles were not poor, then it is sunny. If Charles were poor, then Barbara is rich.
Charles is not poor can be inferred via the modus tollens rule. If Charles were poor, then Barbara is rich can be inferred via the biconditional elimination rule. If Barbara were rich, then Charles is poor can be inferred via the biconditional elimination rule. Charles is not poor can be inferred via the biconditional elimination rule.