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: It is overcast if and only if it is snowing. Barbara is not a janitor. If it snows, then Patricia is listening to a song. If Patricia listens to a song, then Barbara is a janitor.
Patricia is not listening to a song can be inferred via the modus tollens rule. If it snows, then Barbara is a janitor can be inferred via the transitivity rule. If it is overcast, then it is snowing can be inferred via the biconditional elimination rule. If it snows, then it is overcast can be inferred via the biconditional elimination rule.