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, x_5 is not an office clerk. For all x_5, if x_5 were happy, then x_5 is an office clerk. For all x_5, x_5 is happy if and only if x_5 is an office clerk.
For all x_5, x_5 is not happy can be inferred via the universal modus tollens rule. For all x_5, if x_5 were happy, then x_5 is an office clerk can be inferred via the universal biconditional elimination rule. For all x_5, if x_5 were an office clerk, then x_5 is happy can be inferred via the universal biconditional elimination rule. For all x_5, x_5 is not happy can be inferred via the universal biconditional elimination rule.