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_9, x_9 is a mechanic or x_9 will take a plane. There is at least one x_9 for which x_9 is a writer if and only if x_9 will take a plane. For all x_9, if x_9 were an electrician, then x_9 is a writer. For all x_9, x_9 is not a mechanic.
For all x_9, x_9 will take a plane can be inferred via the universal disjunctive syllogism rule. There is at least one x_9 for which if x_9 were a writer, then x_9 is taking a plane can be inferred via the existential biconditional elimination rule. There is at least one x_9 for which if x_9 takes a plane, then x_9 is a writer can be inferred via the existential biconditional elimination rule.