What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? It is overcast if and only if David is taking a plane. It is not overcast. For all x_23, x_23 is not excited. It is sunny if and only if Mary is excited.
If it is overcast, then David is taking a plane. If it is sunny, then Mary is excited. If David takes a plane, then it is overcast. If Mary were excited, then it is sunny. David is not taking a plane.