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 it is overcast, then Jessica is happy. Jessica is not happy. It is overcast if and only if Karen is taking a plane. If Sarah were a writer, then Karen is taking a plane.
It is not overcast can be inferred via the modus tollens rule. If it is overcast, then Karen is taking a plane can be inferred via the biconditional elimination rule. If Karen takes a plane, then it is overcast can be inferred via the biconditional elimination rule.