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: Richard is not sleeping. If it is overcast, then Richard is sleeping. James is taking a plane if and only if it is overcast. It is overcast or Richard is not sleeping.
It is not overcast can be inferred via the modus tollens rule. If Richard sleeps, then it is overcast can be inferred via the rewriting rule. If James takes a plane, then it is overcast can be inferred via the biconditional elimination rule. If it is overcast, then James is taking a plane can be inferred via the biconditional elimination rule.