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: If Barbara works, then it is raining. Robert is rich. It is snowing if and only if it is raining. If Robert were rich, then Barbara is working.
Barbara is working can be inferred via the modus ponens rule. If Robert were rich, then it is raining can be inferred via the transitivity rule. If it snows, then it is raining can be inferred via the biconditional elimination rule. If it rains, then it is snowing can be inferred via the biconditional elimination rule.