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 were a soldier, then x_6 is working. For all x_6, x_6 is not a soldier. For all x_6, if x_6 works, then x_6 is a soldier. For all x_6, if x_6 works, then x_6 is a soldier.
For all x_6, x_6 will not work can be inferred via the universal modus tollens rule. For all x_6, x_6 will not work can be inferred via the universal modus tollens rule. For all x_6, x_6 is a soldier if and only if x_6 will work can be inferred via the universal biconditional introduction rule. For all x_6, x_6 is a soldier if and only if x_6 will work can be inferred via the universal biconditional introduction rule. For all x_6, x_6 will work if and only if x_6 is a soldier can be inferred via the universal biconditional introduction rule. For all x_6, x_6 will work if and only if x_6 is a soldier can be inferred via the universal biconditional introduction rule.