What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? It is late if and only if Mary is an office clerk. It is not late. Mary is an office clerk if and only if Patricia is working.
If it is late, then Mary is an office clerk. If Mary were an office clerk, then Patricia is working. If Mary were an office clerk, then it is late. If Patricia works, then Mary is an office clerk. Mary is not an office clerk.