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 takes a plane, then x_6 is playing tennis. For all x_6, if x_6 plays tennis, then x_6 is a taxi driver. For all x_6, if x_6 plays tennis, then x_6 is taking a plane. For all x_6, x_6 will not take a plane. For all x_6, if x_6 were a taxi driver, then x_6 is playing tennis.
For all x_6, x_6 will not play tennis can be inferred via the universal modus tollens rule. For all x_6, if x_6 takes a plane, then x_6 is a taxi driver can be inferred via the universal transitivity rule. For all x_6, if x_6 were a taxi driver, then x_6 is taking a plane can be inferred via the universal transitivity rule. For all x_6, x_6 will take a plane if and only if x_6 will play tennis can be inferred via the universal biconditional introduction rule. For all x_6, x_6 will play tennis if and only if x_6 is a taxi driver can be inferred via the universal biconditional introduction rule. For all x_6, x_6 will play tennis if and only if x_6 will take a plane can be inferred via the universal biconditional introduction rule. For all x_6, x_6 is a taxi driver if and only if x_6 will play tennis can be inferred via the universal biconditional introduction rule.