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_5, if x_5 takes a plane, then x_5 is a soldier. For all x_5, x_5 is not a soldier. For all x_5, if x_5 were a soldier, then x_5 is taking a plane. For all x_5, if x_5 writes a letter, then x_5 is taking a plane.
For all x_5, x_5 will not take a plane can be inferred via the universal modus tollens rule. For all x_5, if x_5 writes a letter, then x_5 is a soldier can be inferred via the universal transitivity rule. For all x_5, x_5 will take a plane if and only if x_5 is a soldier can be inferred via the universal biconditional introduction rule. For all x_5, x_5 is a soldier if and only if x_5 will take a plane can be inferred via the universal biconditional introduction rule.