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_11, x_11 is an office clerk or x_11 will sleep. For all x_11, if x_11 were an office clerk, then x_11 is a taxi driver. There is at least one x_11 for which x_11 is not a taxi driver.
There is at least one x_11 for which x_11 is not an office clerk can be inferred via the existential modus tollens rule.