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 John is a writer. Thomas is a janitor or it is overcast. Thomas is not a janitor or Mary is listening to a song. If Mary listens to a song, then John is a writer.
It is overcast or Mary is listening to a song. If it is overcast, then John is a writer. If John were a writer, then it is overcast.