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: For all x_9, x_9 is an office clerk. There is at least one x_9 for which x_9 will play tennis. For all x_9, if x_9 takes a plane, then x_9 is an office clerk. For all x_9, if x_9 were an office clerk, then x_9 is taking a plane.
For all x_9, x_9 will take a plane can be inferred via the universal modus ponens rule. There is at least one x_9 for which x_9 will play tennis and x_9 is an office clerk can be inferred via the existential conjunction rule. There is at least one x_9 for which x_9 is an office clerk and x_9 will play tennis can be inferred via the existential conjunction rule. For all x_9, x_9 will take a plane if and only if x_9 is an office clerk can be inferred via the universal biconditional introduction rule. For all x_9, x_9 is an office clerk if and only if x_9 will take a plane can be inferred via the universal biconditional introduction rule.