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: It is not overcast. It is overcast or it is raining. James is taking a plane. If Richard writes a letter, then James is not taking a plane.
Richard is not writing a letter can be inferred via the modus tollens rule. It is raining can be inferred via the disjunctive syllogism rule. It is not overcast and James is taking a plane can be inferred via the conjunction rule. James is taking a plane and it is not overcast can be inferred via the conjunction rule.