What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Mary is writing a letter if and only if it is late. Michael is running if and only if it is late. Michael is running or Mary is writing a letter.
If Mary writes a letter, then it is late. If Michael goes running, then it is late. If it is late, then Mary is writing a letter. If it is late, then Michael is running.