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 Robert takes a plane, then it is snowing. If it snows, then Robert is taking a plane. Robert is taking a plane if and only if it is snowing.
Robert is taking a plane if and only if it is snowing can be inferred via the biconditional introduction rule. It is snowing if and only if Robert is taking a plane can be inferred via the biconditional introduction rule. If Robert takes a plane, then it is snowing can be inferred via the biconditional elimination rule. If it snows, then Robert is taking a plane can be inferred via the biconditional elimination rule.