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 Robert were sad, then it is raining. It is cloudy. If it is sunny, then it is raining. If Jennifer writes a letter, then it is not cloudy. Robert is sad or it is sunny.
Jennifer is not writing a letter can be inferred via the modus tollens rule. It is raining can be inferred via the disjunction elimination rule.