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 sunny if and only if David is listening to a song. Richard is a politician or David is a janitor. For all x_13, if x_13 were a janitor, then x_13 is listening to a song. Richard is not a politician or it is sunny.
David is a janitor or it is sunny can be inferred via the resolution rule. If David were a poet, then Richard is a politician can be inferred via the rewriting rule. If it is sunny, then David is listening to a song can be inferred via the biconditional elimination rule. If David listens to a song, then it is sunny can be inferred via the biconditional elimination rule.