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, x_6 is a scientist. For all x_6, x_6 is fast or x_6 is a cashier. For all x_6, if x_6 works, then x_6 is not a scientist. For all x_6, x_6 is fast if and only if x_6 will work.
For all x_6, x_6 will not work can be inferred via the universal modus tollens rule. For all x_6, if x_6 were fast, then x_6 is working can be inferred via the universal biconditional elimination rule. For all x_6, if x_6 works, then x_6 is fast can be inferred via the universal biconditional elimination rule.