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, x_6 is a police officer. For all x_6, if x_6 were a taxi driver, then x_6 is not a police officer. There is at least one x_6 for which x_6 will make tea if and only if x_6 is a nurse. For all x_6, if x_6 were a nurse, then x_6 is a taxi driver.
For all x_6, x_6 is not a taxi driver can be inferred via the universal modus tollens rule. There is at least one x_6 for which if x_6 makes tea, 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 making tea can be inferred via the existential biconditional elimination rule.