What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Charles drinks water, then it is late. If it is late, then Charles is drinking water. If it is late, then Charles is drinking water.
Charles is drinking water if and only if it is late. Charles is drinking water if and only if it is late. It is late if and only if Charles is drinking water. It is late if and only if Charles is drinking water.