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_8, x_8 will take a plane. For all x_8, x_8 is a mechanic if and only if x_8 is happy. For all x_8, if x_8 were happy, then x_8 is a mechanic. For all x_8, if x_8 were happy, then x_8 is not taking a plane.
For all x_8, x_8 is not happy can be inferred via the universal modus tollens rule. For all x_8, if x_8 were a mechanic, then x_8 is happy can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 were happy, then x_8 is a mechanic can be inferred via the universal biconditional elimination rule.