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, if x_8 makes tea, then x_8 is taking a plane. If Susan makes tea, then William is not a taxi driver. William is a taxi driver. For all x_8, if x_8 takes a plane, then x_8 is making tea.
Susan is not making tea can be inferred via the modus tollens rule. For all x_8, x_8 will make tea if and only if x_8 will take a plane can be inferred via the universal biconditional introduction rule. For all x_8, x_8 will take a plane if and only if x_8 will make tea can be inferred via the universal biconditional introduction rule.