What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it is overcast, then Patricia is writing a letter. If it is cloudy, then Patricia is writing a letter. If Patricia writes a letter, then it is overcast. It is not overcast.
Patricia is not writing a letter. If it is cloudy, then it is overcast. It is overcast if and only if Patricia is writing a letter. Patricia is writing a letter if and only if it is overcast.