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_17 for which x_17 is not a police officer. For all x_17, if x_17 takes a plane, then x_17 is a doctor. For all x_17, if x_17 were a lawyer, then x_17 is taking a plane. For all x_17, if x_17 takes a plane, then x_17 is a lawyer. For all x_17, if x_17 were a doctor, then x_17 is a police officer.
There is at least one x_17 for which x_17 is not a doctor can be inferred via the existential modus tollens rule. For all x_17, if x_17 takes a plane, then x_17 is a police officer can be inferred via the universal transitivity rule. For all x_17, if x_17 were a lawyer, then x_17 is a doctor can be inferred via the universal transitivity rule. For all x_17, x_17 is a lawyer if and only if x_17 will take a plane can be inferred via the universal biconditional introduction rule. For all x_17, x_17 will take a plane if and only if x_17 is a lawyer can be inferred via the universal biconditional introduction rule.