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_10, if x_10 were a mechanic, then x_10 is climbing a mountain. James is not writing a letter. If Barbara climbs a mountain, then James is writing a letter.
Barbara is not climbing a mountain can be inferred via the modus tollens rule.