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_12, if x_12 cooks, then x_12 is sad. There is at least one x_12 for which x_12 is a doctor. For all x_12, if x_12 plays squash, then x_12 is cooking. For all x_12, if x_12 were sad, then x_12 is not a doctor.
There is at least one x_12 for which x_12 is not sad can be inferred via the existential modus tollens rule. For all x_12, if x_12 plays squash, then x_12 is sad can be inferred via the universal transitivity rule.