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_6, if x_6 takes a plane, then x_6 is a server. There is at least one x_6 for which x_6 will take a plane if and only if x_6 is a nurse. For all x_6, if x_6 were a server, then x_6 is a nurse.
For all x_6, if x_6 takes a plane, then x_6 is a nurse can be inferred via the universal transitivity rule. There is at least one x_6 for which if x_6 takes a plane, then x_6 is a nurse can be inferred via the existential biconditional elimination rule. There is at least one x_6 for which if x_6 were a nurse, then x_6 is taking a plane can be inferred via the existential biconditional elimination rule.