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_3, x_3 is not a taxi driver. For all x_3, x_3 is a taxi driver if and only if x_3 is a writer. For all x_3, x_3 is a writer or x_3 is a doctor.
For all x_3, if x_3 were a taxi driver, then x_3 is a writer can be inferred via the universal biconditional elimination rule. For all x_3, if x_3 were a writer, then x_3 is a taxi driver can be inferred via the universal biconditional elimination rule. For all x_3, x_3 is not a writer can be inferred via the universal biconditional elimination rule.