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: It is cold if and only if James is taking a plane. It is not cold. If Robert were a nurse, then James is taking a plane. If James takes a plane, then Robert is a nurse.
Robert is a nurse if and only if James is taking a plane can be inferred via the biconditional introduction rule. James is taking a plane if and only if Robert is a nurse can be inferred via the biconditional introduction rule. If it is cold, then James is taking a plane can be inferred via the biconditional elimination rule. If James takes a plane, then it is cold can be inferred via the biconditional elimination rule. James is not taking a plane can be inferred via the biconditional elimination rule.