What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: If Patricia sleeps, then Mary is a janitor. It is snowing or Mary is not a janitor. It is snowing if and only if Patricia is sleeping. It is not snowing.
Mary is not a janitor can be inferred via the disjunctive syllogism rule. If Mary were a janitor, then it is snowing can be inferred via the rewriting rule. If it snows, then Patricia is sleeping can be inferred via the biconditional elimination rule. If Patricia sleeps, then it is snowing can be inferred via the biconditional elimination rule. Patricia is not sleeping can be inferred via the biconditional elimination rule.