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_9 for which if x_9 takes a plane, then x_9 is making tea. For all x_9, x_9 is an office clerk. For all x_9, if x_9 makes tea, then x_9 is taking a plane. 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 if x_9 were an office clerk, then x_9 is making tea can be inferred via the existential transitivity rule. There is at least one x_9 for which x_9 will take a plane if and only if x_9 will make tea can be inferred via the existential biconditional introduction rule. There is at least one x_9 for which x_9 will make tea if and only if x_9 will take a plane can be inferred via the existential biconditional introduction rule.