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: David is not a janitor. David is a janitor if and only if it is snowing. If it doesn't snow, then it is overcast.
If David were a janitor, then it is snowing can be inferred via the biconditional elimination rule. If it snows, then David is a janitor can be inferred via the biconditional elimination rule. It is not snowing can be inferred via the biconditional elimination rule.