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: There is at least one x for which if x takes a plane, then x is driving a car. For all x, if x drives a car, then x is taking a plane. For all x, if x takes a plane, then x is driving a car.
For all x, x will drive a car if and only if x will take a plane can be inferred via the universal biconditional introduction rule. For all x, x will take a plane if and only if x will drive a car can be inferred via the universal biconditional introduction rule. There is at least one x for which x will take a plane if and only if x will drive a car can be inferred via the existential biconditional introduction rule. There is at least one x for which x will drive a car if and only if x will take a plane can be inferred via the existential biconditional introduction rule.