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: If David plays squash, then it is sunny. It is not sunny. For all x_15, if x_15 were a carpenter, then x_15 is playing squash. If Michael were a sailor, then David is a carpenter.
David is not playing squash can be inferred via the modus tollens rule.